Sustainable Applications of Endophytic Bacteria and Their Physiological/Biochemical Roles on Medicinal and Herbal Plants: Review

Abstract

Bacterial endophytes reside within the tissues of living plant species without causing any harm or disease to their hosts. These endophytes can be isolated, identified, characterized, and used as biofertilizers. Moreover, bacterial endophytes increase the plants’ resistance against diseases, pests, and parasites, and are a promising source of pharmaceutically important bioactives. For instance, the production of antibiotics, auxins, biosurfactants, cytokinin’s, ethylene, enzymes, gibberellins, nitric oxide organic acids, osmolytes, and siderophores is accredited to the existence of various bacterial strains. Thus, this manuscript intends to review the sustainable applications of endophytic bacteria to promote the growth, development, and chemical integrity of medicinal and herbal plants, as well as their role in plant physiology. The study of the importance of bacterial endophytes in the suppression of diseases in medicinal and herbal plants is crucial and a promising area of future investigation.

1. Introduction

It is well known that users of endophytic bacteria employ comparable strategies to enhance plants growth. In addition, endophytic bacteria are more successful than rhizobacteria at reducing the negative impacts of environmental stressors on plants. They enter the plant tissue primarily through the roots and other natural openings in the plant. After entering the plant, bacterial endophytes may spread throughout the tissues of the host plant [1]. Medicinal and herbal plants have secondary metabolites which function as important drugs, flavor, fragrances, agrochemicals, dye, pigments, pesticides, and may play a key role in the adaptation of plants to their environment [2].

Bacterial endophytes of the genera Bacillus, Pantoea, Pseudomonas, Stenotrophomonas, and Serratia can produce phytohormones, such as auxin and gibberellin, as well as protease and hydrogen cyanide, and play a role in siderophore production, phosphate solubilization, and atmospheric nitrogen fixation [3]. Among other endophytes, Bacillus, Pseudomonas, Agrobacterium, and Flavobacterium species solubilize the inorganic phosphate compounds by phosphatases. Bacterial species of the genera Alcaligenes, Arthrobacter, Azotobacter, Bradyrhizobium, Chromobacterium, Enterobacter, Escherichia, Micrococcus, Streptomyces, Serratia, and Thiobacillus secrete organic acids to solubilize the insoluble phosphorus. Pseudomonas spp. and Bacillus spp. are known endophytes that are involved in siderophores production [4]. For example, secondary metabolites produced by endophytic bacterium Bacillus pumilus have a significant inhibitory effect against fungal species, such as Pythium aphanidermatum, Rhizoctonia solani, and Sclerotium rolfsii [5]. The leaf and stem of heart-leaved moonseed (Tinospora cordifolia (Thunb.) Miers) contain Bacillus, Aneurinibacillus, and Pseudomonas species [6]. Traditional medicine has long utilized T. cordifolia to treat several conditions including fever, jaundice, chronic diarrhea, cancer, dysentery, bone fractures, pain, asthma, skin diseases, deadly bug bites, and eye issues.

Nitrogen-fixing bacterial strains are linked with certain leguminous and non-leguminous species [7]. Species such as Gluconacetobacter diazotrophicus and Azorhizobium caulinodans can fix nitrogen [8]. Pseudomonas putida, Azospirillum brasilense, and Enterobacter cloacae enable plants to grow and survive under higher levels of polyaromatic hydrocarbons (PAHs) through phytoremediation [9]. Arthrobacter sp. and Bacillus sp. bacterial endophytes produce secondary metabolites for plants to adapt to abiotic stress [10]. Several studies have shown that endophytic bacteria play a beneficial role in plant growth. It is not yet clear which bacterial strains contribute more to the growth and development of medicinal plants. It is well-known that the density of endophytic bacteria within the plant tissues is less than that of found in the rooting zone [11]. Plant-growth-promoting (PGP) bacteria that fix nitrogen may be used as biofertilizers to improve plant growth [12]. Many of these bacteria also produce phytohormones [13]—for example, as the bacterial strain SCCPVE07—that improve the growth of coriander (Coriandrum sativum L.) grown under salinity stress [14]. The stem and leaves of coriander have antimicrobial and antibacterial qualities. Inoculated C. sativum showed higher levels of calcium, carbon, iron, and potassium contents. In this case, the levels of cinnamic acid, 4-methoxy-cinnamic acid hexoside, 5-O-caffeoylquinic acid, K-3-O-rutinoside, Q-3-O-rutinoside, Q-3-O-glucoside, and Q-3-O-glucuronide were significantly increased [15]. In addition, certain plant species are capable of accumulating heavy metals and soil contaminants in their tissues [16].

In this context, we aim to provide a review of the sustainable applications of endophytic bacteria and their physiological and biochemical processes on m medicinal and herbal plants to lay a foundation for future studies intended for the isolation, identification, and characterization of endophytic bacteria from the internal tissues of medicinal and herbal plants. Understanding these functions might lead to the development of new techniques in agricultural and biotechnological environments, specifically for the future cultivation and commercialization of indigenous medicinal and herbal plants.

2. Potentialities of Endophytic Bacteria

In this regard, this research thoroughly examines several bacterial endophytes and their potentialities on herbal plant species without inflicting any harm or disease to their hosts, drawing on a variety of sources in the literature. These endophytes can be isolated, recognized, and characterized in addition to being employed as biofertilizers to improve plant development and change the chemical makeup of the plant. Additionally, bacterial endophytes boost plants’ resilience to diseases, pests, and parasites and are a promising source of bioactives with the potential for use in pharmaceuticals (Figure 1). For instance, the existence of distinct bacterial strains is credited with the synthesis of antibiotics, auxins, biosurfactants, cytokinins, ethylene, enzymes, gibberellins, nitric oxide organic acids, osmolytes, and siderophores. In order to enhance the growth, development, and chemical integrity of medicinal and herbal plants, as well as their function in plant physiology, this manuscript reviews sustainable applications of endophytic bacteria. It is critical to examine the role of bacterial endophytes in the control of illnesses in medicinal and herbal plants—a promising avenue of future research.

2.1. Growth-Promoting through Nitrogen Fixation, Phosphate Solubilization and Anti-Pathogenic Capabilities

Endophytic bacteria have been increasingly associated with the ability to suppress a broad pool of plants diseases, with this ability being closely associated with the vegetative growth and chemical composition of the plant [17]. Different alkaloids contribute to plant defense through endophytes action, acting as growth-promoting compounds or having a key role in plants’ resistance to environmental stress. Amines and amides, very common metabolites from endophytes, present toxic activities against insects. Steroids, terpenoids, and diterpenes are also generated by endophytes [18] and are responsible of several activities such as plant-growth promotion and yield, suppression of pathogen-growth and colonization, contaminants remotion, phosphate solubilization, and nitrogen plant-assimilation [19]. These properties may be helpful in organic tea plantation [20,21].

Pseudomonas and Bacillus spp. were studied for their role against blister blight disease caused by Exobasidium vexans in tea plants [22]. Pseudomonas fluorescens, applied at 7-day intervals, reduced the disease incidence for two seasons to the same level as a fungicide and increased tea yield. Chemical analysis of the plant showed that there was induction of phenolics compounds and defense enzymes, such as peroxidase, polyphenol oxidase, phenylalanine ammonia lyase, chitinase, and β-1,3-glucanase. Methylobacterium radiotolerans MAMP 4754 was isolated and identified from the seeds of the therapeutic plant Combretum erythrophyllum in order to explore the endophyte’s antibacterial and antioxidant properties [23]. Basil (Ocimum sanctum L.) plants have antimicrobial, immunomodulatory, antistress, anti-inflammatory, antipyretic, anti-asthmatic, hypoglycaemic, hypotensive, and analgesic properties [24,25].

Endophytes living within a healthy plant are a good source of antimicrobial agents, enzymes, and secondary metabolites [24]. For example, endophytic bacterial strains isolated from O. sanctum leaf tissues are antagonistic to pathogenic fungi, such as Alternaria solani, Fusarium solani, R. solani, S. rolfsii, and Colletotrichum lindemuthianum [26], and are therefore capable of promoting the O. sanctum growth. Interestingly, O. sactum treatment with these bacterial endophytes increased the content of plant essential oil, with this demonstrated influence of bacterial endophytes on O. sactum growth and oil content [26]. Bacterial endophytes inhibited six out of ten test microorganisms [24]. Among these, Salmonella typhi, which is a typhoid-causing bacterium, was significantly inhibited by 3 bacterial isolates (BTS 2, GTL 3, BTS 4), while 2 bacterial isolates (BTS 2, GTL 3) significantly inhibited Micrococcus luteus, an opportunistic pathogen. Medicinal species, such as seepweed (Suaeda nudiflora Thwaites), white-flowered black mangrove (Lumnitzera racemose Willd.), beach moonflower (Ipomoea tuba (Schltdl.) Colla), and mangrove (Avicennia alba Blume) have different levels of antimicrobial activities against M. luteus, Pseudomonas aeruginosa, Staphylococcus aureus, Klebsella pneumonia, and Bacillus subtilis [27].

In China, Glycyrrhiza spp. are regarded as the most important herbs to treat blood disorders, cancer, and hepatitis, and these plant species are thought to improve the immune system while reducing chemotherapy-related side effects [28]. Glycyrrhiza spp. have antimicrobial activity [29]. Licorice (Glycyrrhiza glabra L.) is a perennial shrub that contains glabridin which is specifically derived from the plant’s roots [30]. G. glabra is used to manage ulcer and respiratory problems [31]. Licorice (Glycyrrhiza uralensis Fisch. ex DC) is a leguminous herb that is native to Asia [32], but it is now grown in many parts of the world [32]. The roots of G. uralensis produce a variety of terpenoids and flavonoids. Bacterial strains were isolated from the root nodules of G. uralensis and G. glabra to identify and classify them, as well as to determine their level of stress tolerance [30,32]. Based on 113 physiological and biochemical characteristics, the isolates were clustered into three groups. One bacterial isolate, which belongs to the genus Mesorhizobium, has a high tolerance to NaCl, pH, and high temperatures.

Nodulation tests demonstrated that this isolate also formed nitrogen-fixing nodules on other plants, namely sophora (Sophora viciifolia Hance), bird’s-foot trefoil (Lotus corniculatus L.), white clove (Trifolium repens L.), melilot (Melilotus suaveolens Ledeb.), and bitter licorice (Sophora alopecuroides L.). S. alopecuroides has been used as a traditional Chinese medicine to treat fever and diarrhea, among other diseases, as well as to inhibit cancer cell growth [33,34]. 16S rRNA and recA gene analyses revealed the presence of Agrobacterium tumefaciens, Mesorhizobium alhagi, Mesorhizobium gobiense, Mesorhizobium amorphae, Phyllobacterium trifolii, Rhizobium giardinii, Rhizobium indigoferae, Sinorhizobium fredii, and Sinorhizobium meliloti from the root nodules of S. alopecuroides in different regions of China’s Loess Plateau [35].

Ginger (Zingiber officinale Roscoe) is an important medicinal plant, producing aromatic rhizomes which are valuable both as spice and herbal medicine [36]. Ginger has been used as a traditional medicine in China and India for more than 25 centuries [37]. However, ginger wilt provoked by Ralstonia solanacearum is a severe disease which threatens the productivity of ginger in China. Ginger has anti-inflammatory, anti-emetic, and chemo-protective properties [38]. Bacterial strains were isolated from the plant surface as well as the stem, leaf, and root tissues of Z. officinale for their antimicrobial activity against R. solanacearum using amplified ribosomal DNA restriction analysis (ARDRA) fingerprint analysis [36]. It was also found that the isolated bacterial strains had the ability to produce certain enzymes and metabolites which exert a significant reduction in disease occurrence when the antagonists were applied.

Rooibos tea (Aspalathus linearis (Burm.f.) R.Dahlgren) is the source of commercialized rooibos tea, which is endemic in the mountains of the Western Cape province in South Africa [39]. Burkholderia tuberum was originally isolated from Aspalathus sp. (rooibos tea plant) nodules in South Africa [40]. Sequence analysis of the 16S rRNA showed that endophytic bacterial isolates were beta-rhizobia [39]. Rooibos tea contains no colorants, additives, or preservatives and is free of caffeine. Bush tea (Athrixia phylicoides DC.) is indigenous to Southern Africa. A. phylicoides is used for cleansing or purifying blood, treating boils, headaches, infected wounds, and cuts [41,42]. Vhavenda people believe bush tea has aphrodisiac properties [43]. Traditionally, Zulu people prefer bush tea decoction extracted from the root as a cough remedy and purgative [44], whereas the Sotho people use bush tea as a soothing wash for sore feet [45,46]. It is known that leaves of bush tea contain 5-hydroxy-6,7,8,3′,4′,5′-hexamethoxy flavon-3-ol [41,47], 3-O-demethyldigicitrin; 5,6,7,8,3′,4′-hexamethoxyflavone and quercetin [48], total polyphenols [41,48,49], tannins [49], and total antioxidants [50,51,52].

Echinacea spp. contain polysaccharides, glycoproteins, alkamides, volatile oils, and flavonoids [53]. The echinacea herb is used for the treatment of flu and colds [54]. Endophytic bacteria of the genera Acinetobacter, Bacillus, Pseudomonas, Wautersia (Ralstonia), and Stenotrophomonas were identified and characterized from the medicinal plant Echinacea spp. by means of 16S rRNA gene analyses and other microbiological tests such as thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). It was also discovered that the Pseudomonas stutzeri P3 strain produces the plant indole acetic acid [40]. In terms of antibiotic resistance, it was found that most endophytic bacterial isolates were resistant to the antibiotic kanamycin.

Bacillus, Brachybacterium, Kocuria, Leucobacter, Lysinibacillus, Mycobacterium, Paenibacillus, Pseudomonas, Providencia, Rhizobium, and Streptomyces have been isolated from Polygonum cuspidatum Sieb. et Zucc. and identified using 16S rDNA sequence. P. cuspidatum produces polydatin, a glycosylated derivative of resveratrol. These endophytic bacteria isolated from P. cuspidatum have inhibitory activity against Aspergillus niger, Aspergillus fumigatus, B. subtilis, Gibberella fujikuroi, K. pneumoniae, and S. aureus [55]. From the roots and leaves of Radish (Raphanus sativus L.) at Jinju, Korea, Proteobacteria, Bacillus, and Bacteroidetes spp. were isolated using phylogenetic analysis based on 16S rDNA sequences. B. subtilis exhibited amylase, cellulase, xylanase, mannase, PGAase, DNase, protease, and esterase and inhibitory action against plant pathogenic fungi [56]. In China, R. sativus is used to treat hypertension, chronic tracheitis, and constipation.

Extract of endophytes isolated from creat or green chiretta (Andrographis paniculata (Burm. f.) Wall. ex Nees) contains antibacterial activities against human pathogenic bacteria [57]. From internal tissues of the root and stem of Piper nigrum L., endophytic bacterial species such as Pseudomonas spp., Serratia spp., Bacillus spp., Arthrobacter spp., Micrococcus spp., and Curtobacterium sp. (1 strain) were isolated and identified based on 16S rDNA sequencing and found to be effective antagonistic endophytes for the biological control of Phytophthora capsici [58]. White Tree Peon (Paeonia ostia T. Hong and J.X.Zhang) is an important medicinal plant of China, and 56 endophytic bacterial strains were identified by 16S rDNA gene sequence analysis. These bacterial endophytes contain non-ribosomal peptide synthetase and putative polyketide synthase genes responsible for bioactivities [59].

Pseudomonas aeruginosa isolated from balloon flower (Platycodon grandiflorum (Jacq.) A. DC.) degraded 2,4-Dichlorophenoxyacetic acid which is responsible for antimicrobial activity against pathogenic fungus causing balloon flower root rot [60]. Endophytic bacteria isolated from the leaves of pennywort (Centella asiatica (L.) Urb.), B. subtilis BCA31, and P. fluorescens BCA08 reduced the growth rate and disease incidence of the causal agent of anthracnose Colletotrichum higginsianum [61]. The endophyte B. subtilis ALB629 isolated from cacao seedlings has antimicrobial properties against fungi Moniliophthora perniciosa and Colletotrichum gossypii. B. subtilis ALB629 promotes growth of both the aerial and roots of cacao seedlings [62]. 16S rRNA sequence analysis revealed Bacillus, Streptomyces, Pseudovibrio, and Pseudomonas species isolated from Rhizophora stylosa. These isolates had antimicrobial activity against E. coli ATCC 25922, P. aeruginosa ATCC 25923, B. subtilis ATCC 27212, S. aureus ATCC 12,222, and C. albicans ATCC 7754 [63].

Dendrobium spp. are medicinal plants containing properties with anti-cancer, anti-fatigue, gastric ulcer protective effects, etc. Of all the bacterial endophytes isolated from stems of Dendrobium spp. plants, Bacillus megaterium exhibited the highest antimicrobial effects [64]. Acinetobacter guillouiae, B. cereus, Burkholderia tropica, Novosphingobium sp., Pseudomonas moraviensis, Pseudomonas sp., Rahnella aquatilis, and Raoultella ornithinolytica, were isolated from the Cape coast lily (Crinum macowanii Baker) bulbs and showed potential for possible drug lead against common pathogenic bacteria [65]. Traditional uses of C. macowanii include treating boils, diarrhea, fever, inflammation, respiratory issues, skin rashes, tuberculosis, wounds, and urinary tract issues. Bacterial isolates FjR1 and FjF2 from the Indian coffee plum (Flacourtia jangomas (Lour.) Raeusch.) displayed potential antimicrobial activity against pathogenic bacteria [66]. The longevity spinach (Gynura procumbens DC.) is a medicinal plant species for treatment of cancer, constipation, fever, kidney diseases, rheumatism, rashes, headache, and viral skin diseases [67,68]. The leaves of G. procumbens contain anti-herpes simplex virus, antihyperglycemic, anti-inflammatory, antihyperlipidemic, anti-allergy agent, and antihypertensive properties [68]. Apart from its antihypertensive, glucose-lowering, and anti-inflammatory properties, it is also a source of proteins and peroxidase [69]. G. procumbens leaves contain essential oil, flavonoids, miraculin, polyphenols, peroxidase, thaumatin-like proteins, terpenoids, and unsaturated sterols. The screening of endophytic bacteria for the plant growth regulators such as cytokinin were needed as means to explore if these endophytic bacteria can be applied in agriculture [67]. Acenitobacter calcoaceticus, Paenibacillus polymaxa, and Psuedomonas resinovorans were isolated from G. procumbens leaves collected in Malaysia [68]. It was also found that broth extracts from P. resinovorans and P. polymaxa contain cytokinin-like compounds [68].

Acetone extract from kauri booti (Ajuga bracteosa Wall ex Benth.) has antibacterial activity against E. coli [70]. This plant contains phytochemicals which have anti-inflammatory, astringent, diuretic, and depurative properties, and can be used to treat agues, menorrhea, bronchitis, diarrhea, fever, gout, jaundice, pneumonia, palsy, and rheumatism [71]. The leaves, bark, stem, and roots of A. bracteosa have medicinal properties, can be used as an astringent against hypoglycaemic and gastrointestinal disorders, and have anthelmintic, diuretic, antifungal, anti-inflammatory, and antimycobacterial compounds [71]. Bacterial species were isolated and screened for PGP and biotechnological potential associated with A. bracteosa, with most isolates belonged to Proteobacteria and Pseudomonas [70,71]. These isolates exhibited PGP through production of siderophores and indole acetic acid. They are also capable of phosphate solubilization through production of hydrolytic enzymes such as amylase, cellulose, chitinase, lipase, pectinase, phosphatase, and protease [71].

The biological compounds produced by endophytic bacteria play a pivotal role in the protection of medicinal and herbal plants against pests and pathogens (

Table 1. Endophytic bacteria with antimicrobial activity and associated secondary metabolites from medicinal and herbal plant species.

Isolated Bacterial Species	Biochemical/Physiological Activity	Host Medicinal Plant Species	Host Plant Part/Region	References
Pseudomonas sp., Bacillus sp., Enterobacter sp., Pantoea sp., Chryseobacterium sp., Sphingobacterium sp., Aeromonas sp., Providencia sp., Cedecea sp., Klebsiella sp., Cronobacter sp., Macrococcus sp., Shigella sp.	1,1-diphenyl-2-picrylhydrazyl, ascorbic acid production	Aloe vera	Stem, leaf, root	[72]
Streptomyces sp., Micromonospora sp., Microbiospora sp., Nocardia sp.	Coronamycin, hydroxamate type siderophores production	Azadirachta indica	Stem, leaf, root	[73]
Bacillus sp., Bacillus megaterium, Bacillus pumilus, Bacillus licheniformis, Micrococcus luteus, Paenibacillus sp., Pseudomonas sp., Acinetobacter calcoaceticus	Amylase, esterase, lipase, protease, pectinase, xylanase, and cellulose production	Plectranthus tenuiflorus	Stem, leaf, root	[74]
21 endophytic bacteria	Amines, amides, acids, quinines, indole derivatives, steroids, azoles, alcohols, and hydrocarbons production	Cleodendrum myricoides, Lannea flavus, Dichrostachys cinerea, Gomphocarpus fruticosus, Balanites aegyptica, Jasminium floribundum, Hibiscus fuscus	Root	[75]
Bacillus polyfermenticus, Bacillus subtilis, Bacillus licheniformis, Bacillus pumilus	Cellulase production, Xylanase production, annanase production Pectinase, Amylase, Protease, Lipase, Esterase, DNase, Chitinase production	Codonopsis lanceolata	Root	[76]
Bacillus amyloliquefaciens	diethyl ether, ethyl acetate production	Memecylon edule, Tinospora cordifolia, Phyllodium pulchellum, Dipterocarpus tuberculatus	Whole plant	[77]
Bacillus spp.	NM	Rumex pulcher	Leaf, stem	[78]
Bacillus amyloliquefaciens	diethyl ether; chloroform and ethyl acetate production	Tinospora cordifolia, Phyllodium pulchellum, Dipterocarpus tuberculatus		[77]
Bacillus spp.	NM	Hypericum scabrum	Leaf	[78]
Bacillus licheniformis, Bacillus pumilus	cellulase, xylanase, mannase, pectinase, amylase, protease, lipase, esterase, DNase, linchinase, chitinase production	Platycodon grandiflorum	Root	[79]
Bacillus sp., Paenibacillus sp., Pseudomonas sp., Ralstonia sp., Micrococcus sp., Alcaligenes spp.	Catalase, Amylase, Gelatinase, Lipase, Nitrate Reductase, Dextrose, Fructose, Lactose, Maltose and Sucrose production	Paederia foetida	Leaf, stem	[80]
Streptomyces griseus	p-Aminoacetophenonic acids production	Kandelia candel	NM	[81]
Serratia marcescens	Oocydin A production	Rhyncholacis penicillata	NM	[82]
Streptomyces spp.	Munumbicins, Munumbicin D production	Kennedia nigriscans	NM	[83]
Paenibacillus polymyxa	Fusaricidin A–D production	Arabidopsis thaliana, Canola spp.	NM	[84]
Streptomyces sp.	Coronamycin production	Monstera sp.	NM	[85]
Phyllobacterium sp.	Fatty acids production	Epimedium brevicornum	Stem, root	[86]
Streptomyces sp.	Indolosesquiterpenes, xiamycin, indosespene, sespenine production	Kandelia candel	Stem	[87]
Streptomyces sp.	Xiamycin production	Bruguiera gymnorrhiza	Stem	[88]
Saccharopolyspora flava, Pseudonocardia zijingensis, Nocardia carnea, Streptomyces hainanensis, Polymorphospora rubra, Janibacter melonis, Nocardiopsis dassonvillei, Glycomyces sambucus	NM	Maytenus austroyunnanensis	Root	[89]
Gordonia sputi, Gordonia polyisoprenivorans, Microbacterium paraoxydans, Nocardiopsis dassonvillei, Jiangella alkaliphila, Tsukamurella tyrosinosolvens	NM	Maytenus austroyunnanensis	Stem	[89]
Saccharopolyspora gregorii	NM	Gloriosa superba	Stem	[89]
Amycolatopsis pretoriensis	NM	Saccharopolyspora gregorii	Root	[89]
Lentzea albida	NM	Ficus tikoua	Root	[89]
Pseudonocardia alni	NM	Callicarpa longifolia	Leaf	[89]
Pseudonocardia kongjuensis	NM	Lobelia clavata	Leaf	[89]
Rhodococcus fascians	NM	Cercidiphyllum japonicum	Leaf	[89]
Micromonospora narashino, Micromonospora peucetia, Promicromonospora aerolata, Arthrobacter mysorens, Actinomadura atramentaria, Nonomuraea candida	NM	Mycobacterium monacense	Leaf	[89]
Dietzia maris	NM	Schima sp.	Stem	[89]
Dietzia natronolimnaea	NM	Cercidiphyllum japonicum	Root	[89]
Streptomyces specialis	NM	Sedum sp.	Root	[89]
Blastococcus aggregatus, Dactylosporangium aurantiacum	NM	Tripterygium wilfordii	Root	[89]
Catellatospora chokoriensis	NM	Berberis chingii	Root	[89]
Kineosporia aurantiaca, Saccharopolyspora flava	NM	Tripterygium wilfordii	Stem	[89]
Promicromonospora sukumoe	NM	Cymbopogon citratus	Root	[89]
Oerskovia jenensis	NM	Ginkgo sp.	Leaf	[89]
Micrococcus flavus	NM	Polyspora axillaris	Root	[89]
Micrococcus flavus	NM	Aquilaria sinensis	Root	[89]
Actinocorallia aurantiaca	NM	Duranta repens	Root	[89]
Actinocorallia herbida	NM	Millettia reticulata	Leaf	[89]
Herbidospora cretacea	NM	Osyris wightiana	Stem	[89]
Glycomyces algeriensis	NM	Carex baccans	Root	[89]
Glycomyces algeriensis	NM	Scoparia dulcis	Root	[89]
Unidentified bacterial endophytes (gram positive)	Amines, amides, acids, quinines, indole derivatives, steroids, azoles, alcohols, hydrocarbons production	Cleodendrum myricoides, Lannea flavus, Dichrostachys cinerea, Gomphocarpus fruticosus, Balanites aegyptica, Jasminium floribundum, Hibiscus fuscus	Root	[89]
Lysinibacillus sp., Paenibacillus sp., Pseudomonas sp., Bacillus sp., Kocuria sp., Streptomyces sp., Providencia sp., Rhizobium sp., Leucobacter sp., Brachybacterium sp., Mycobacterium sp.	fengycins, surfactants production	Polygonum cuspidatum	Root	[55]
Enterobacter sp., B. subtilis	amylase, cellulase, xylanase, mannase, PGAase, DNase, protease, and esterase production	Raphanus sativus	Leaf, root	[55]
Bacillus spp.		Andrographis paniculata	Leaves	[57]
Pseudomonas spp., Serratia sp., Bacillus sp., Arthrobacter sp., Micrococcus sp., Curtobacterium sp.		Piper nigrum	Root, stem	[58]
Bacillus amyloliquefaciens	Bacteriocins production	Bruguiera gymnorrhiza	Leaf	[90]
Bacillus thuringiensis, B. pumilus		Suaeda monoica, Suaeda maritima, Salicornia brachiata, Lumnitzera racemosa, Sesuvium portulacastrum, Rhizophora apiculata, Rhizophora mucronata, Bruguiera cylindrica, Ceriops decandra, Avicennia marina, Aegiceras corniculatum	Leaf	[91]
Paenibacillus sp.	Cellulases, xylanases, pectinase, fusaricidin, peptide synthetase, lipopeptides, and bacitracin production	Aloe chinensis	Root	[92]
Actinomadura sp., Amycolatopsis sp., Dactylosporangium sp., Kocuria sp., Kribbella sp., Micrococcus sp., Micromonospora sp., Nonomuraea sp., Promicromonospora sp., Pseudonocardia sp., Rhodococcus sp., Streptomyces sp., Streptosporangium sp.	Antibiotics production	Artemisia annua	Leaf, stem, root	[93]
Streptomyces sp., Streptosporangium sp., Microbispora sp., Streptoverticillium sp., Sacchromonospora sp., Nocardia sp.	Munumbacin A-D, Kakadumy, Coronamyncin production	Azadirachta indica	Leaf, stem, root	[94]
Bacillus sp., Enterobacter sp., Streptomyces sp.	NM	Paeonia ostii	Root	[95]
Pseudomonas aeruginosa	2,4-Dichlorophenoxyacetic acid ichlorophenoxyacetic acid, Phenazone production	Platycodon grandiflorum	Root	[79]
Paenibacillus polymyxa, Bacillus sp., Pseudomonas poae	Cellulase, xylanase, pectinase production	Panax ginseng	Root	[96]
Bacillus amyloliquefaciens subsp. Plantarum, Bacillus methylotrophicus	NM	Panax notoginseng	root, stem, Petiole, leaf, seed	[97]
Bacillus subtilis, Pseudomonas fluorescens	Iturin A, surfactant production	Centella asiatica	Leaf	[98]
Arthrobacter sp., Achromobacter sp., Bacillus sp., Enterobacter sp., Erwinia sp., Pseudomonas sp., Pantoea sp., Serratia sp., Stenotrophomonas sp.	Cellulase, protease, β-1,3-glucanase, hydrogen cyanide production	Hypericum perforatum	Root, stem, leaf	[99]
Achromobacter sp., Bacillus sp., Enterobacter sp., Erwinia sp., Pseudomonas sp., Pantoea sp.	Cellulase, Protease, β-1,3-glucanase, hydrogen cyanide production	Ziziphora capitata	Root, stem, leaf	[99]
Pseudomonas hibiscicola, Macrococcus caseolyticus, Enterobacter ludwigii, Bacillus anthracis	1,1-diphenyl-2-picrylhydrazyl production	Aloe vera	Root, stem, leaf	[72]
B. tequilensis, Pseudomonas entomophila, Chryseobacterium indologenes, B. aerophilus	Ascorbic acid production	Aloe vera	Root, stem, leaf	[72]

NM = not mentioned.

). Living plants are a good source for bacterial endophytes which can be isolated for more efficient production of antimicrobial compounds with pharmacological importance. In turn, medicinal plants could also benefit in terms of growth promotion with less application of inputs such as fertilizers, fungicides, insecticides, or herbicides.

2.2. Growth-Promoting Bacteria on Medicinal and Herbal Plants

Sixty-one bacteria were identified and comparatively characterized from the root nodules of Medicago, Melilotus Onobrychis, Oxytropis, and Vicia species grown in the Loess Plateau and Qinghai-Tibet Plateau [100]. Vicia sativa has been used as a traditional medicine to treat asthma, bronchitis, skin infections, and urinary diseases, and it also has anti-poison, antiseptic, aphrodisiac, antipyretic, and antirheumatic properties [101]. Oxytropis spp. contain flavonoids, alkaloids, and saponins which have medicinal properties [102]. Apigenin, caffeic acid, gallic acid, pyrogallol, salicylic acid, naringenin, quercetin, myricetin, and daidzein are major secondary metabolites in the extract of the alfalfa (Medicago sativa L.) leaves [103]. Melilotus spp. are native to the Mediterranean area [104]; their herbs have aromatic, emollient, and carminative properties [105]. Onobrychis genus is an important legume with over 150 species [106]. Among the bacterial isolates are Rhizobium leguminosarum, S. meliloti, and S. fredii; the rest belong to Mesorhizobium, Phyllobacterium, and Stenotrophomonas. Species of R. leguminosarum was isolated from Oxytropis spp. and medick or burclover (Medicago archiducis-nicolai Širj.), while S. fredii was isolated from the black medick (Medicago lupulina L.) grown in the Qinghai-Tibet Plateau. These strains were also found to be resistant to high alkalinity and a high concentration of NaCl [100]. V. sativa contains significant activity against pathogenic bacterial species such as Bacillus atrophaeus, E. coli, S. aureus, and Staphylococcus epidermidis [101]. Medicago spp. are used to treat eczema, anemia, constipation, body odor, infections, burns, athlete’s foot, cancer, arthritis, intestinal ulcers, gastritis, liver diseases, bleeding gums, and high blood pressure.

The hyacinth bean (Lablab purpureus (L.)) serves as a herbal medicine in China for the treatment of internal heat fever. The leaves and fruits of L. purpureus contain sterols and fatty acids such as palmitic, palmitoleic, linoleic, and linolenic acids [104,107,108]. Pyridine alkaloids, trigonelline, and sterols have been isolated from tissue cultures of seeds, stems, and leaves. To study the diverse rhizobia associated with this plant, Bradyrhizobium, Rhizobium, Ensifer, and Mesorhizobium species were isolated from southern China [104].

Based on 16S rDNA analysis, the bacteria isolated belonged to Aeromonas, Bacteroides. Cytophaga, Flexibacter, Ilyobacter, Pelomonas, Proteobacteria, Pseudomonas, Rhodoferax, Rhizobium, Sulfurospirillum, and Uliginosibacterium. These endophytic bacteria have the capacities of fixing nitrogen and removal of contaminants from the water body through phytoremediation by degrading catechol, cyanide, methane, methanol, methylated amines, oxochlorate, urea, and 2,4-Dichlorophenoxyacetic acid [109]. Although this area of study will not form part of our investigation, we may opportunistically assess the possibility of environmental remediation by bacteria when we survey natural populations of A. phylicoides.

Caragana spp. are leguminous plants containing more than 80 species worldwide [110]. The roots, flowers, shoots, barks, and seeds are useful plant parts applied as herbal medicine [111] for the treatment of cancer of gynecological problems [112]. Species of the genus Caragana are resistant to extreme temperatures and have nitrogen-fixing abilities [110]. Agrobacterium, Mesorhizobium, Rhizobium, Bradyrhizobium, and Phyllobacterium species are associated with Caragana species grown in China [110].

Bacterial species belonging to Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria phyla are salinity tolerant nitrogen-fixing endophytic bacteria isolated from roots of the halophyte Suaeda sp. obtained in Iran and are capable of growth–promotion the halophyte sea-blite (Suaeda maritima (L.) Dumort.) [113]. Nitrogen-fixing bacteria of Brachybacterium saurashtrense sp. nov., Zhihengliuella sp., Brevibacterium casei, Haererehalobacter sp., Halomonas sp., Vibrio sp., Cronobacter sakazakii, Pseudomonas spp., Rhizobium radiobacter, and Mesorhizobium sp. were isolated and identified from roots of halophytic pickleweed (Salicornia brachiatas Miq.) using analysis of 16S rRNA genes. It has been revealed that isolated endophytic bacteria from S. brachiatas is capable of growth promotion based on production of indole acetic acid production, phosphate solubilization, and 1- aminocyclopropane-1-carboxylic acid deaminase [114].

Using 16 S rDNA, it was discovered that the root nodules of Mimosa patida contains Burkholderia spp. that secretes phytohormone, aminocyclopropane-1-carboxylic acid deaminase, and solubilizes phosphate and has antimicrobial activity against phytopathogens [115]. Azotobacter beijerinckii, Azotobacter chroococcum, Azospirillum lipoferum, and Azotobacter vinelandii isolated from the roots of medicinal aloe (Aloe vera (L.) Burm.f.) and devil’s trumpet (Datura metel L.) fix nitrogen. These isolates also secrete glucose, sucrose, lactose, maltose, rhamnose, xylose, and mannitol. The production of indole acetic acid by A. beijerinckii, A. chroococcum, and A. vinelandii stimulated the growth of A. vera and D. metel [116].

The root nodules of sulla (Hedysarum carnosum L.), clover bord (Hedysarum spinosissimum L.), and Hedysarum pallidum Desf., sampled from various localities in Algeria, were isolated based on the ARDRA, Random Amplified Polymorphic DNA (RAPD) fingerprinting, and 16S rDNA have, E. cloacae, Enterobacter kobei, Escherichia vulneris, Leclercia adecarboxylata, Pantoea agglomerans and Pseudomonas sp. [117]. Rhizobium tropici isolated had nitrogen-fixing symbioses with Medicago ruthenica [118]. Both the isolation and characterization of Rhizobium, Sinorhizobium, Mesorhizobium, and Bradyrhizobium species from Acacia, Anthyllis, Argyrolobium, Astragalus, Calycotome, Coronilla, Ebenus, Genista, Hedysarum, Hippocrepis, Lathyrus, Lotus, Medicago, and Ononis species from southern Sudan were based on comparative 16S ARDRA using seven enzymes, total cell protein sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) analysis, and 16S rDNA sequencing [119].

Rhizobium huautlense, a nitrogen-fixing rhizobial symbionts of bigpod sesbania (Sesbania herbacea (Mill.) McVaugh), sampled at Sierra de Huautla, Mexico, was isolated and identified using PCR-RFLP analysis. The electrophoretic alloenzyme types (Ets) were also identified [120]. R. indigoferae sp. nov. and Sinorhizobium kummerowiae sp. nov from root nodules of Indigofera spp. and Kummerowia spp.; R. loessense sp. nov from the root nodules of Astragalus and Lespedeza spp; and R. sullae sp. nov were described as the nitrogen-fixing bacterial symbionts [121,122,123]. The multi-locus enzyme electrophoresis (MLEE) and 16S rRNA gene sequence analysis revealed two nitrogen fixing bacterial species of Sinorhizobium arboris sp. nov. and Sinorhizobium kostiense sp. nov. from the root nodules of Acacia rutico and Prosopis chilensis sampled in Sudan and Kenya [124].

Sinorhizobium morelense sp. nov. isolated from root nodules of jumbay (Leucaena leucocephala (Lam.) de Wit) has been found to be resistant to carbenicillin, kanamycin, and erythromycin [125]. This medicinal plant is frequently used to treat diabetes. It is also used to treat stomach ailments, assist abortion, and promote contraction. The revealed Allorhizobium undicola sp. nov. solated from the water mimosa or sensitive Neptunia (Neptunia natans (Girard) Kuntze) based on the 16S rRNA gene sequencing has nitrogen-fixing ability [126]. This medicinal plant has pharmacological qualities that include antifungal, antiemetic, astringent, anthelmintic, antidysentery, diuretic, anti-inflammatory, antioxidant, hypercholesterolemia, antipyretic, and antiemetic properties.

From nodules of False Indigo (Amorpha fruticose L.), M. amorphae sp. nov was characterized based on the RFLP of PCR-amplified 16S rRNA genes, MLEE, DNA–DNA hybridization, 16S rRNA gene sequencing, electrophoretic plasmid profiles, cross-nodulation, and a phenotypic study [127]. A. fruticose is used to treat dermatitis, carbuncles, and burns in traditional Chinese medicine. DNA–DNA hybridizations were conducted to identify Mesorhizobium spp. from the sample from the white carob tree (Prosopis alba Griseb.) root nodules grown in Argentina [128]. R. tropici were found to be root modulating bacteria of N. natans from India [129]. Prosopis plants have a variety of bioactive qualities, including antioxidant, anti-inflammatory, anti-cancer, and anti-diabetic properties.

A new species name for a root-forming nodule bacterial isolate, Devosia neptuniae sp. nov., which was previously classified as A. undicola, was suggested to neptunium-modulating rhizobia isolated from India. This bacterial species can form a bonafide dinitrogen-fixing root-nodule symbiosis with other legume plants [130].

Root-nodule isolates of Bradyrhizobium, Mesorhizobium, Rhizobium, and Sinorhizobium spp. from Lespedeza spp., collected from China and the USA, were isolated and characterized using SDS-PAGE analysis of whole-cell proteins, DNA–DNA hybridization, and 16S rRNA gene sequence analysis [131]. Ralstonia taiwanensis sp. nov. was isolated from Mimosa spp. and is the capable of root nodule formation and nitrogen fixation [132].

The endophytic bacterial isolates from H. carnosum, H. spinosissimum subsp. capitatum, and H. pallidum grown in Algeria were identified as P. agglomerans, E. kobei, E. cloacae, L. adecarboxylata, E. vulneris, and Pseudomonas sp. by means of ARDRA using the enzyme Cfo I, RAPD fingerprinting and sequencing of 16S rDNA. This was the first report confirming that Gammaproteobacteria is associated with H. carnosum, H. spinosissimum subsp. Capitatum, and H. pallidu [117]. The diversity of endophytic bacteria from the root of Angelica sinensis in Angelica in the Gansu province revealed that certain endophytic bacterial strains may have come from the rooting zone [133].

Among the endophytic bacteria isolated from the red clover (Trifolium pratense L.), P. agglomerans (59.6%) was mostly detected in foliage tissues, Agrobacterium rhizogenes A in the tap root (49.2%), and R. leguminosarum BV phaseoli and R. loti B in the nodules (27.2% each) [134]. In addition, T. pratense has been used medicinally to treat a number of illnesses, such as eczema and psoriasis, cancer, whooping cough, respiratory issues, and skin inflammations. B. megaterium, Bordetella avium, Curtobacterium luteum, and R. leguminosarum BV trifolii promoted the growth of T. pratense. Nodulation of red clover seedlings became evident because of co-inoculation of R. leguminosarum BV trifolii with Bacillus insolitus, B. brevis, or A. rhizogenes A [134]. Crop rotations of T. pratense and potato (Solanum tuberosum L.) have specific associations with bacterial endophytes. Of all the growth-promoting bacterial strains isolated from these plants, 63% enhanced shoot height, 66% enhanced shoot wet weight, and 55% enhanced root wet weight [135]. It has been claimed that potatoes offer a multitude of medicinal properties, including antioxidant, anticancer, antiallergy, antibacterial, anti-inflammatory, anti-obesity, and anti-ulcer action. A total of 200 bacterial isolates from the berseem clover (Trifolium alexandrinum L.) possess plant growth promoting traits. Production of indole acetic acid by the endophytic bacteria stimulated the plant development of rice plant [136]. Because of their expectorant, analgesic, and antibacterial qualities, Trifolium spp. are also used to treat rheumatic pains. Co-inoculation of T. repens with Rhizobium strains CHB1120 and CHB1121, Bacillus aryabhattai strain Sb, and A. vinelandii strain G31 promotes the nitrogen fixation and nutrient uptake of white clover in a P-deficient soil [137].

Nitrogen-fixing bacteria can form endophytic colonies in various medicinal and herbal plants. These beneficial bacteria fix nitrogen from the atmosphere to enhance the length and biomass of medicinal and herbal plants. Nitrogen-fixing endophytic bacteria may be useful for the sustainable production of medicinal and herbal plants, specifically in saline-based environments. Nitrogen-fixing bacteria are currently being introduced as biofertilizers.

Native phosphate-solubilizing endophytic bacteria, including those from rhizospheres, improve the growth of herbal and medicinal plants. Various leaf structural and chemical characteristics were assessed as possible predictors of the size of the phyllosphere bacterial population associated with plant species such as strawberry tree (Arbutus unedo L. 1753), lesser calamint (Calamintha nepeta (L.) Kuntze), rockrose (Cistus × incanus L.), lavender (Lavandula stoechas L.), lemon balm (Melissa officinalis L.), common myrtle (Myrtus communis L.), lentisk or mastic (Pistacia lentiscus L.), and kermes oak (Quercus coccifera L.) [57]. A. unedo contain polyphenols, which are reported to manage cancer risk, coronary heart disease, and other degenerative diseases [58]. Quercus spp. have been used as traditional medicinal plants and are antiseptic and hemostatic for the treatment of diarrhea and hemorrhoids [59]. Certain species of the genus Quercus contain antimicrobial, anti-inflammatory, gastroprotective, antioxidant, cytotoxic, and antitumor properties [59]. The extract of the different parts of P. lentiscus has antiatherogenic, anti-inflammatory, antioxidant, antimicrobial, hypotensive, anticancer, anti-arthritis, antigout, anti-asthmatic, and anthelmintic activities [60]. M. communis is used for various ailments such as diarrhea, dysentery, gastric ulcers, hemorrhages, leucorrhea, rheumatism, sinuses, and vomiting [61]. Lavender oils are derived from the true lavender (Lavandula angustifolia Mill.), Spanish lavender (Lavandula stoechas L.), broadleaved lavender (Lavandula latifolia Medik.) and lavender (Lavandula × intermedia ‘Grosso’) [62], which have antimicrobial, anti-inflammatory, hypnotic, and anxiolytic properties [63]. C. × incanus contains phenolic substances together with an associated strong antioxidant activity [64]. C. nepeta is aromatic, diaphoretic, expectorant, febrifuge, and stomachic [65]. M. officinalis possesses antioxidants such as caffeic and rosmarinic acids [66]. M. officinalis also contains antibacterial and antiviral properties. The role of the P-solubilizing bacterium Enterobacter ludwigii in the growth promotion and P content of barley (Hordeum vulgare L.) was investigated [138].

The study revealed beneficial effects on the dry weight, P assimilation, and barley yield in E. ludwigii-inoculated plants [138]. C. nepeta, M. communis, M. officinalis, and L. stoechas produce essential oils Interestingly, aromatic plants are more colonized than the other species, whereas the non-woody perennials are more highly colonized than the water pepper (Polygonum hydropiper (L.) Delabre 1800) is regarded as a P-accumulating herb used for P-phytoextraction, with higher P-accumulating capability in the mining ecotype compared to the non-mining ecotype [139]. In traditional medical systems, water pepper is used as an astringent, sedative, antiseptic, and to treat respiratory problems, edema, and snake bites.

Tea plant (Camellia sinensis (L.) Kuntze) is used in one of the most important beverages; the plant contains about 4000 bioactive compounds, of which 1/3 is contributed by polyphenols alone [140]. The phytochemical screening of green tea showed the presence of alkaloids, saponins, tannins, catechin, and polyphenols [56,141], which are quality parameters of tea. A study was conducted to examine the diversity of cultivable P-solubilizing bacteria in C. sinensis [142]. Over 900 rhizoplane bacteria were randomly selected and were identified using fatty acid methyl ester (FAME) analysis and isolates belonging to Bacillus (34.6%), Pseudomonas (8.9%), Stenotrophomonas (6.1%), Paenibacillus (5.9%), and Arthrobacter (4.8%) were identified [2]. The leaf of C. sinensis showed antimicrobial properties against S. aureus, Vibrio cholerae, C. jejuni, S. epidermidis, V. mimicus, L. monocytogenes, E. coli, S. typhi, P. aeruginosa, H. pylori, and P. acnes, among others [143,144,145,146,147,148,149,150,151,152]. Proteobacteria and Sphingobacteria spp. possess plant growth promoting attributes such as indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase production, and P and K-solubilization [153].

Aloe (Aloe barbadensis Mill.) is an important medicinal plant with applications in pharmaceutical, food, and cosmetic industries and is used for flavoring liquid formulations [154]. A. barbadensis contains phenolic compounds such as aloin-A (barbaloin), aloesin, soaloeresin D, and aloeresin E used in the treatment of tumors, diabetes, ulcers, and cancer [155]. Burkholderia gladioli, Enterobacter hormaechei, Pseudomonas synxantha, and S. marcescens isolated from A. barbadensis are capable of solubilizing phosphate into liquid phase [154]. From Brassica juncea (L). Czern and Coss var. Pusa Bold (DIR-50), a Ni-tolerant B. subtilis strain SJ-101 was isolated and identified. It was found that the strain SJ-101 produced indole acetic acid and solubilized inorganic phosphate [55]. Endophytic bacteria isolate from P. hydropiper contains plant growth promotion traits including indole acetic acid, siderophores, and phosphate-solubilization among others [156]. Endophytic bacterial strains isolated from the tissues of livening thyme (Thymus vulgaris L.) exhibited some plant growth-promoting activities such as auxin synthesis, diazotrophic, P-solubilization, siderophore production, and production of lytic enzymes (i.e., chitinase, cellulase, protease, and lipase) under in vitro conditions [157]. T. vulgaris has been used for treating chest congestion and promoting salivation since ancient times. The fresh leaves are also consumed to soothe sore throats.

Endophytic bacteria are capable of solubilizing inorganic phosphate in a solid medium, thereby increasing its availability to living medicinal and herbal plants (

Table 2. Growth-promoting bacteria and associated secondary metabolites from medicinal and herbal plant species.

Isolated Bacterial Species	Biochemical/Physiological Activity	Host Medicinal Plant Species	Host Plant Part/Region	References
Enterobacter sp. strain 638, Stenotrophomonas maltophilia R551-3, Pseudomonas putida W619, Serratia proteamaculans 568	Root/ biomass development	Populus spp.	Root and shoot	[158]
Bradyrhizobium sp.	Increased Nitrogen and phosphorus uptake	Cicer arietinum	Root	[159]
Mesorhizobium ciceri	Increased Nitrogen and phosphorus uptake	Vigna radiata	Root	[160]
Rhizobium sp.	Indole acetic acid	Cajanus cajan	Root	[161]
Bradyrhizobium sp.	Increased uptake of P, N and Mg High chlorophyll content	Vigna radiata	Root	[162]
Methylobacterium sp.	NM	Crotalaria glaucoides	Root	[163]
Azotobacter sp., Azospirillum sp.	indole acetic acid production	Aloe vera	Root	[164]
Pantoea agglomerans, Enterobacter kobei, Enterobacter cloacae, Leclercia adecarboxylata, Escherichia vulneris	NM	Hedysarum carnosum, H. spinosissimum subsp. capitatum, H. pallidum	Root	[117]
Rhizobium leguminosarum	NM	Pisum sativum, Vicia sp., Lathyrus sp., Lens sp., Trifolium pratense, Trifolium spp., Phaseolus vulgaris, P. angustifolius, P. multiflorus	NM	[165]
R. elti biovar phaseoli	NM	Phaseolus vulgaris, Leucaena sp.	NM	[166]
R. etli biovar mimosae	NM	Mimosa affinis	NM	[167]
R. hainanense	NM	Desmodium sinuatum, Desmodium gyroides, Desmodium triquetrum, Desmodium heterophyllum, Acacia sinicus, Arachis hypogaea, Centrosema pubescens, Macroptilium lathyroides, Stylosanthes guianensis, Tephrosia candida, Uraria crinita, Zornia diphylla	NM	[168]
R. gallicum biovar gallicum	NM	Phaseolus vulgaris, Leucaena leucocephala, Macroptilium atropurpureum, Onobbrychis viciifolia	NM	[168]
R. gallicum biovar phaseoli	NM	Phaseolus vulgaris	NM	[168]
R. mongolense	NM	Medicago ruthenica, Phaseolus vulgaris	NM	[168]
R. galegae biovar orientalis	NM	Galega orientalis	NM	[168]
R. galegae biovar officinalis	NM	Galega officinalis, Astragalus cruciatus, Argyrolobium uniflorum, Anthyllis henoniana, Lotus creticus, Medicago spp.	Root	[168]
R. giardinii biovar giardinii	NM	Leucaena leucocephala, Macroptilium atropurpureum	NM	[168]
R. giardinii biovar phaseoli	NM	Phaseolus vulgaris	NM	[168]
R. huautlense	NM	Sesbania herbacea	NM	[168]
R. indigoferae	NM	Indigofera amblyantha, I. carlesii, I. potanini	NM	[168]
R. sullae	NM	Hedysarum coronarium	NM	[168]
R. loessense	NM	Astragalus sp., Lespedeza sp.	NM	[168]
R. yanglingense	NM	Coronilla varia, Amphicarpaea trisperma, Gueldenstaedtia multiflora	NM	[168]
Sinorhizobium meliloti	NM	Medigaco sp., Melilotus sp., Trigonella sp.	NM	[168]
S. sahelense	NM	Sesbania sp., Acacia sp.	NM	[168]
S. terangae	NM	Acacia sp., Sesbania sp.	NM	[168]
S. medicae	NM	Medicago sp.	NM	[168]
S. kostiense	NM	Acacia sp., Prosopis sp.	NM	[168]
S. morelense	NM	Leucaena leucocephala	NM	[168]
S. americanum	NM	Acacia sp.	NM	[168]
S. arboris	NM	Acacia sp., Prosopis sp.	NM	[168]
S. kummerowiae	NM	Kummerowia stipulacea	NM	[168]
Ensifer adhaerens	NM	Sesbania sp., Medicago sp., Sesbania grandiflora, Leucaena leucocephala, Pithecellobium dulce, Medicagosativa sp.	NM	[168]
Allorhizobium undicola	NM	Neptunia natans, Acacia senegal, A. seyal, A tortilis, Lotus arabicus, Faidherbia albida	NM	[168]
Mesorhizobium loti	NM	Lotus corniculatus, L. tenuis, L. japonicum, L. krylovii, L. filicalius, L. schoelleri, Anthyllis spp., Lupinus spp.	NM	[168]
M. huakuii	NM	Astragalus sinicus, Acacia spp.	NM	[168]
M. ciceri	NM	Cicer arietinum	NM	[168]
M. tianshanense	NM	Glycyrrhiza pallidiflora, G. uralensis, Sophora alopecuroides, Glycine max, Swainsonia salsula, Halimodendron holodendron, Caragana polourensis	NM	[168]
M. mediterraneum	NM	Cicer arietinum	NM	[168]
M. plurifarium	NM	Acacia senegal, A. seyal, A. tortilis, Leucaena leucocephala, L. diversifolia, Prosopisjuliflora, Chamaecrista ensiformis	NM	[168]
M. amorphae	NM	Amorpha fruticosa	NM	[168]
M. chacoense	NM	Prosopis alba	NM	[168]
Methylobacterium nodulans	NM	Crotalaria podocarpa, C. Perottetti, C. glaucoides.	NM	[168]
Ochrobactrum spp.	NM	A. mangium, Faidherbia albida, Paraserianthes falcataria	NM	[168]
Devosia neptuniae	NM	Neptunia natans	NM	[168]
Azorhizobium caulinodans	NM	Sesbania rostrata	NM	[168]
A. johannense	NM	Sesbania virgata	NM	[168]
Azorhizobium sp.	NM	Sesbania rostrata	NM	[168]
Bradyrhizobium japonicum	NM	Glycine max, Glycine soja, Macroptilium atropurpureum	NM	[168]
B. elkanii	NM	Glycine max, Vigna spp., Macroptilium atropurpureum	NM	[168]
B. liaoningense	NM	Glycine max, Glycine soja	NM	[168]
B. yuanmingense	NM	Lespedeza cuneata	NM	[168]
B. betae	NM	Beta vulgaris	NM	[168]
B. canariense	NM	Genisteae and Loteae plants	NM	[168]
Bradyrhizobium sp.	NM	Lupinus spp., Mimosa spp., Faidherbia spp., Acacia spp., 27 herb legumes	NM	[168]
Blastobacter denitrificans	NM	Aeschynomene indica	NM	[168]
Burkholderia caribensis	NM	Mimosa pudica, M. diplotricha	NM	[168]
B. tuberum	NM	Alysicarpus glumaceus	NM	[168]
B. phymatum	NM	Aspalatus carnosa Machaerium lunatum	NM	[168]
Ralstonia taiwanensis	NM	Mimosa pudica, M. diplotricha.	NM	[168]
Pantoea agglomerans	NM	Hedysarum carnosum, H. spinosissimum subsp. capitatum, H. pallidum	NM	[168]
Enterobacter kobei	NM	Hedysarum carnosum, H. spinosissimum subsp. capitatum, H. pallidum	NM	[168]
Enterobacter cloacae	NM	Hedysarum carnosum, H. spinosissimum subsp. capitatum, H. pallidum	NM	[168]
Leclercia adecarboxylata	NM	Hedysarum carnosum, H. spinosissimum subsp. capitatum, H. pallidum	NM	[168]
Escherichia vulneris	NM	Hedysarum carnosum, H. spinosissimum subsp. capitatum, H. pallidum	NM	[168]
Pseudomonas sp.	NM	Hedysarum carnosum, H. spinosissimum subsp. capitatum, H. pallidum	NM	[168]
Pseudomonas sp.	Indole acetic acid, hydrogen cyanide, and siderophore production	Solanum sp.	Rhizosphere	[169]
Enterobacter aerogenes NBRI K24, Rahnella aquatilis NBRI K3	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, siderophore production	Brassica juncea	NM	[170]
Enterobacter sp.	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, siderophore production	Brassica juncea	NM	[170]
Pseudomonas aeruginosa	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, siderophore production	Solanum nigram	NM	[171]
Bacillus thuringiensis GDB-1	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, Siderophores, Phosphate solubilization	Alnus firma	Root, shoot	[172]
B. pumilus E2S2, Bacillus sp. E1S2	indole acetic acid, ACC deaminase, siderophores, phosphate solubilization	Sedum plumbizincicola	Root, shoot	[172]
Pseudomonas tolaasii ACC23, P. fluorescens ACC9	ACC deaminase, siderophores indole acetic acidproduction	B. napus	Root, shoot	[172]
Pseudomonas veronii	indole acetic acid, decrease soil pH, supply P, and Fe	S. alfredii	Root, shoot	[172]
Rhizobium indigoferae sp. nov. and Sinorhizobium kummerowiae sp.	NM	Indigofera spp. and Kummerowia stipulacea	Root	[121]
Achromobacter xylosoxidans Ax10	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acidproduction; P solubilization	B. Juncea	Root, shoot	[172]
Psychrobacter sp. SRA1, Bacillus cereus SRA10	Aminocyclopropane-1-carboxylic acid deaminase indole acetic acid, P solubilization	B. Juncea	Root, shoot	[172]
Pseudomonas sp. SRI2, Psychrobacter sp. SRS8, Bacillus sp. SN9	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid production; P solubilization,	B. Juncea	Root, shoot	[172]
Pseudomonas sp. SRI2, Psychrobacter sp. SRS8, Bacillus sp. SN9	Aminocyclopropane-1-carboxylic acid deaminase indole acetic acid production; P solubilization	Brassica oxyrrhina	Root, shoot	[172]
Bacillus subtilis, B. cereus, B. megaterium, Pseudomonas aeruginosa	Improve plant growth and root elongation	Orychophragmus violaceus	Root, shoot	[172]
Pantoea agglomerans Jp3-3, Pseudomonas thivervalensis Y1-3-9	Indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production; phosphate solubilization	B. napus	Root, shoot	[172]
Enterobacter sp. JYX7, Klebsiella sp. JYX10	Indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production, phosphate solubilization	Polygonum pubescens	Root, shoot	[172]
Rahnella sp.	Indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production; phosphate solubilization	Amaranthus hypochondriacus, A. mangostanus, Solanum nigrum	Root, shoot	[172]
Kluyvera ascorbata SUD165	Increased biomass; Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
K. ascorbata SUD165, SUD165/26	Increased biomass; Aminocyclopropane-1-carboxylic acid deaminase, siderophores production	Brassica juncea	NM	[172]
Enterobacter cloacae CAL2	Increased biomass; Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	Enterobacter cloacae CAL2	[172]
B. subtilis SJ-101	Indole acetic acid production; phosphate solubilization	Brassica juncea	NM	[172]
Enterobacter sp. NBRI K28	Increased biomass; indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production; phosphate solubilization	Brassica juncea	NM	[172]
Bacillus sp. J119	Increased biomass, indole acetic acid, siderophores production; biosurfactant production	Brassica napus	NM	[172]
P. aeruginosa MKRh3	Increased biomass and rooting, indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production; phosphate solubilization	Vigna mungo	NM	[172]
Bacillus sp. J119	I indole acetic acid, siderophores production; biosurfactant production	Brassica napus	NM	[172]
Pseudomonas sp. M6, Pseudomonas jessenii M15	Increased biomass; indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase production; phosphate solubilization	Ricinus communis	NM	[172]
Achromobacter xylosoxidans Ax10	Increased root and shoot length and biomass; aminocyclopropane-1-carboxylic acid deaminase production; phosphate solubilization, indole acetic acid production	Brassica juncea	NM	[172]
Enterobacter aerogenes, Rahnella aquatilis	Increased biomass and metal uptake; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production, phosphate solubilization	Brassica juncea	NM	[172]
B. subtilis SJ-101	indole acetic acid, P solubilization	Brassica juncea	NM	[172]
P. putida ARB86	Increased biomass and chlorophyll content	Arabidopsis thaliana	NM	[172]
Bradyrhizobium sp. RM8	Increased growth, seed yield, seed protein, nodule number, plant nutrition, indole acetic acid, siderophores, hydrogen cyanide, ammonia production	Vigna mungo	NM	[172]
Rhizobium sp. RP5	Increased biomass, nodule number and plant nutrition, indole acetic acid, siderophores production	Pisum sativum	NM	[172]
Enterobacter sp. NBRI K28	Increased biomass, protein, and chlorophyll content, indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production; P solubilization	Brassica juncea	NM	[172]
Pseudomonas sp. 29C, Bacillus sp. 4C	Increased biomass; indole acetic acid, siderophores production, Aminocyclopropane-1-carboxylic acid deaminase, P solubilization	Brassica juncea	NM	[172]
Pseudomonas sp. M6, Pseudomonas jessenii M15	Increased biomass; indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase production; P solubilization	Ricinus communis	NM	[172]
Pseudomonas sp.	Increased biomass; siderophores production	Cicer arietinum	NM	[172]
Enterobacter erogenes, Rahnella aquatilis	Increased biomass, indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production, P solubilization	Brassica juncea	NM	[172]
Psychrobacter sp. SRA1 and SRA2, Bacillus cereus SRA10	Increased biomass, indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production. P solubilization	Brassica juncea, B. oxyrrhina	NM	[172]
Rahnella sp. JN6	Indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase, siderophores, phosphate solubilization	B. napus	Root, shoot	[172]
Psuedomonas aspleni	Increased biomass; indole acetic acid production	Brassica napus	NM	[172]
Variovorax paradoxus, Rhodoccus sp., Flavobacterium sp.	Increased root length; indole acetic acid, siderophores, production Aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Pseudomonas fluorescens, P. putida	Increased seed germination and growth	Brassica napus	NM	[172]
P. putida UW4, P. putida HS-2	Increased biomass in the field; indole acetic acid, Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Sinorhizobium sp. Pb002	Aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Azotobacter chroococcum HKN-5, B. megaterium HKP-1, B. mucilaginosus HKK-1	Increased biomass	Brassica juncea	NM	[172]
Pseudomonas sp. RJ10, Bacillus sp. RJ16	Increased biomass; indole acetic acid production	Brassica napus	NM	[172]
Mesorhizobium huakuii subsp. rengei B3	Phytochelatin and metallothionein production	Astragalus sinicus	NM	[172]
Burkholderia cepacia	Increased biomass	Sedum alfredii	NM	[172]
P. putida ARB86	Increased biomass and chlorophyll content	Arabidopsis thaliana	NM	[172]
P. putida HS-2	Increased seed germination and biomass; siderophores, indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Pseudomonas sp. 29C, Bacillus sp. 4C	Increased biomass; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production; phosphate solubilization	Brassica juncea	NM	[172]
Proteus vulgaris KNP3	Increased germination, biomass, and chlorophyll	Cajanus cajan	NM	[172]
Pseudomonas sp.	Increased biomass siderophores production	Cicer arietinum	NM	[172]
P. fluorescens G10, Microbacterium sp. G16	Increased biomass; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Bacillus edaphicus NBT	Increased biomass; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Flavobacterium sp.	Increased root length, biomass	Orychophragmus violaceus	NM	[172]
Kluyvera ascorbata SSUD165	Increased biomass; aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
K. ascorbata SUD165, SUD165/26	Increased biomass; aminocyclopropane-1-carboxylic acid deaminase, siderophores production	Brassica napus	NM	[172]
P. fluorescens, P. putida	Increased seed germination and growth	Brassica napus	NM	[172]
P. putida HS-2	Increased seed germination and biomass; siderophores, indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Different endophytic bacteria	Na+/K+ accumulation	Salicornia, Arthrocnemum, Haloxylon, Sesuvium, Suaeda, Aeluropus, Heleochloa, Atriplex, and Salvadoraet	shoot and root	[173]
Pseudoalteromonas maricaloris	1-aminocyclopropane-1-carboxylic acid Deaminase production	Avicennia marina	Rhizosphere	[174]

NM = not mentioned.

). Phytochemicals released by endophytic bacteria promote the sustainable production of medicinal and herbal plants resulting from improved fertility of the soil, and hence increase medicinal and herbal plant production.

2.3. Endophytic Bacterial Species Responsible for Phytomediation on Medicinal/Herbal Plants

Due to a variety of industrial activities as well as natural processes, the accumulation of heavy metals in soil has rapidly grown. Endophytic bacteria can be isolated from leaves, stems, and roots of plants grown in contaminated soil. Many endophytes are capable of degrading organic contaminants and heavy metals, and can therefore be used for phytoremediation on contaminated soils [175]. The mobility and bioavailability of heavy metals in the soil influence phytoextraction and phytostabilization [16,155]. Plant tolerance to the contamination is crucial for successful phytoremediation [176]. Decontamination may be accelerated with appropriate microorganisms’ inoculation that is able to break down pollutants and compete with indigenous microorganisms.

Yellowtop (Alyssum murale Waldst. and amp; Kit.) is regarded as a metal hyperaccumulator plant and is able to solubilize Ni. A. murale has been used in combination with other medicinal plants for gynecological disorders. It has also been found that Microbacterium oxydans AY509223 increased Ni uptake of A. murale [177]. NBRI K28 Enterobacter sp. also has aminocyclopropane-1-carboxylic acid deaminase activity and increased the growth of the brown mustard (Brassica juncea (L.) Czern.) plants. NBRI K28 Enterobacter sp. enhanced phytoextraction of metals of Ni, Zn, and Cr accumulated by B. juncea [178,179]. P. putida strain PS9, isolated from the turnip (Brassica campestris L.), solubilized phosphate and produced significant amount of salicylic acid, 2,3-dihydroxy benzoic acid, and indole acetic acid [180]. Antioxidant, antibacterial, and anticancer properties are present in Brassica spp.

A considerable number of bacterial strains have been isolated from heavy metal-polluted soil in Nanjing, China, which promoted plant growth and cadmium uptake in rape [Brassica napus L.) [181]. Some of these bacterial isolates had the potential to solubilize cadmium carbonate in solution culture. It has been also confirmed that these cadmium-resistant isolates exhibit the presence of indole acetic acid. These bacterial isolates colonized and developed in B. napus after root inoculation [181]. P. fluorescens G10 and Microbacterium sp. G16 were isolated and identified by means of 16S rDNA gene sequence analysis from the roots of B. napus grown in Pb-contaminated soils. There was significant increase in root elongation of inoculated B. napus seedlings. Endophytic bacterium JN6 isolated from roots of the drooping knotweed (Polygonum pubescens Blume) was identified as Rahnella sp. This showed very high Cd, Pb, and Zn tolerance and effectively solubilized CdCO3, PbCO3, and Zn3(PO4)2 in culture solution [10]. Microbacterium sp. G16 produced indole acetic acid, siderophores, and 1-amino cyclopropane-1-carboxylate deaminase [181]. It has been demonstrated that P. pubescens works well as a traditional Chinese medicine. The Proteobacteria, Actinobacteria, and Bacteroidetes Chloropid isolated from the goat willow (Salix caprea L.) were resistant to Zn/Cd as they produced aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, and siderophores [182]. The leaves S. caprea are made into a decoction which is used to cure fevers. The isolated Bradyrhizobium sp. (vigna) RM8 from nodules of V. radiata sampled from nickel and zinc in India promoted the growth of the host plant [183]. This was evidently shown by the increase in nodule numbers, leghaemoglobin, seed yield, grain protein, root N, and shoots.

Using HPLC analysis, Enterobacter sp. was isolated from the long-stamen onion (Allium macrostemon Bunge) plants grown in polycyclic aromatic hydrocarbon-contaminated soils [184]. This bacterial species also promoted the growth of wheat and maize and removed pyrene from pyrene-amended soil in pot experiments. Enterobacter sp. produced indole acetic acid, siderophore, and solubilize inorganic phosphate. A. macrostemon has historically been used to alleviate thoracic pain, stenocardia, heart asthma, and diarrhea. Bacillus sp., isolated from the roots of venboksal (Alnus firma Siebold and Zucc.) using 16S rRNA sequence analysis, demonstrated the capacity to produce siderophores and indole acetic acid. There was increased root elongation of inoculated B. napus seedlings [185]. The isolates facilitated the capability of reducing heavy metal phytotoxicity and increasing Pb accumulation in A. firma. Alnus spp. are well recognized for their traditional medical uses, which include treating conditions including cancer, hepatitis, uterine cancer, rheumatism, and dysentery, as well as causing stomachaches, diarrhea, and fever. The bacterial population associated with T. caerulescens subsp. calaminare sampled had Zn and Cd capabilities due to the increased availability of the metals in soils near the roots [186]. Based on 16S rRNA sequence analysis, Methylobacterium spp., Rhodococcus spp., and Okibacterium spp. were isolated from the pennycress (Thlaspi goesingense Halácsy) accumulated Ni in ultramafic soils. These isolates produced 1-amino cyclopropane-1-carboxylic acid deaminase and siderophore [187]. Four groups of heavy metal-resistant bacterial such as Actinobacteria, Proteobacteria, Bacteroidetes, and Firmicutes were isolated from the roots, stems, and leaves of black nightshade (Solanum nigrum L.) [188]. These isolates were re-inoculated into S. nigrum under Cd stress which resulted in Cd phytotoxicity decrease. S. nigrum has historically been used to treat bacterial infections, coughs, and indigestion. An endophytic bacteria Serratia sp. RSC-14 isolated from the roots of S. nigrum displayed phosphate solubilization and produced indole acetic acid [189].

Endophytic bacteria associated with the roots, stems, and leaves of Alyssum bertolonii Desv. sampled from central Italy influenced plant growth [190]. These endophytic bacteria also shown potential for nickel-hyperaccumulation There was significant increase in biomass and metal accumulation. Cupriavidus taiwanensis TJ208 isolated from the bashful (Mimosa pudica L.) removed Pb, Cu, and Cd from polluted soils [191]. Since ancient times, M. pudica has been administered topically to heal wounds as well as urogenital disorders, piles, dysentery, and sinuses. Bacillus thuringiensis GDB-1 enhanced growth of A. firma, through production of aminocyclopropane-1-carboxylic acid deaminase activity, indole acetic acid, and siderophores; as well as P solubilization. B. thuringiensis GDB-1 also accumulated As, Cu, Pb, Ni, and Zn in seedlings of A. firma [192]. Zn-tolerant bacterial strains such as B. subtilis, B. cereus, Flavobacterium sp., and P. aeruginosa, isolated from the Chinese violet cress (Orychophragmus violaceus (L.)), significantly increased the shoot biomass and Zn accumulation in O. violaceus [3]. On the other hand, B. subtilis, B. cereus, B. megaterium, and P. aeruginosa isolated from O. violaceus significantly enhanced growth plant and Cd accumulation [193]. O. violaceus oil can be used to make a variety of cosmetic products for the care of the skin, hair, and lips, as well as to make external preparations for the treatment of burns. The diversity of endophytic bacteria associated with the root, stem, and leaf of Poplus sp. enhanced phytoremediation on localities contaminated with BTEX compounds [194].

From S. nigrum grown in metal-polluted soil, Acinetobacter sp. LSE06, Enterobacter aerogenes LRE17, Enterobacter sp. LSE04, and Serratia nematodiphila LRE07 isolates possesses aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, siderophores, and P solubilizing activity. Acinetobacter sp., E. aerogenes, Enterobacter sp., and S. nematodiphila significantly increased Cd extraction from the soils [195]. From a pot experiment Pseudomonas sp. Lk9 isolated from S. nigrum produces biosurfactants, siderophores, and organic acids [196]. Serratia sp. isolated from S. nigrum was resistant to the toxic effects of heavy metals through the production of indole acetic acid, siderophore, and solubilized mineral phosphate [197]. Species of Microbacterium, Arthrobacter, Agreia, Bacillus, Sthenotrophomonas, Kocuria, and Variovorax isolated from the roots of Noccaea caerulescens displayed significant increases in shoot biomass, root length, and root-to-shoot Ni translocation [198]. B. pumilus E2S2 isolated from the stonecrop (Sedum plumbizincicola X.H.Guo and S.B.Zhou ex L.H.Wu) improved its phytoextraction capacity [199]. Common stonecrop is used by people for a variety of things, including coughing, high blood pressure, and wound healing. Endophytic bacterial species isolated from the Chinese brake (Pteris vitata L.) and the spider brake (Pteris multifida Poir.) improved arsenic tolerance and speciation in plants [200]. Pteris spp.’s bioactive potential includes some cytotoxic, anticancer, antiproliferative, neuroprotective, wound-healing, antibacterial, antiviral, hepatoprotective, leishmanicidal, trypanocidal, antinociceptive, anti-inflammatory, immunomodulatory, and chemopreventive properties.

Root-colonizing beneficial bacteria can improve plant growth through resistance to biotic and abiotic stresses. Drought is an environmental condition affecting the productivity of medicinal plants globally. PGP rhizobacteria produce secondary metabolites that could relief drought stress in plants [201]. Pseudomonas pseudoalcaligenes and B. pumilus have a significant ability to withstand adverse effects caused by saline stress [202].

In vitro inoculation of grapevine (Vitis vinifera L.) explants with Burkholderia phytofirmans increased grapevine growth and physiological activity at a low temperature [203]. Root zone bacterial species such as Arthrobacter, Azotobacter, Azospirillum, Bacillus, Enterobacter, Pseudomonas, Serratia, and Streptomyces produce compounds that benefit living plants through abiotic stress relief [204]. Streptomyces coelicolor, S. geysiriensis, and S. olivaceus are drought tolerant plants grown in arid and drought-affected regions [205]. It has been established that proanthocyanidin-rich V. vinifera seed extract protects against a wide range of illnesses, including infections, cancer, diabetes, hypertension, peptic ulcers, and cardiovascular disease. These endophytic actinobacteria produce phytohormones, contain PGP traits, and have the water-stress tolerance potential to promote growth plants grown in stressed environments. P. fluorescens and B. subtilis isolated from V. radiata produce water-stress-related proteins and enzymes [206]. B. saurashtrense and Pseudomonas sp. isolated from Salicornia brachiate significantly increased the host’s growth under salt stress conditions [55]. Methylobacterium sp. (strain BJ001) isolated from Populus deltoides × nigra DN34 degraded 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazene (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX) [56,158]. Rheumatism, arthritis, lower back pains, urinary complaints, digestive and liver problems, debility, anorexia, fevers, and menstrual cramp discomfort are all traditionally treated with Populus spp. [207]. Bacillus, Pseudomonas, Klebsiella, Serratia, Arthrobacter, Streptomyces, Isoptericola, and Microbacterium species isolated from the leaves, stems and roots of sea lavender (Limonium sinense (Girard) Kuntze) produced Aminocyclopropane-1-carboxylic acid deaminase and indole acetic acid. They are also capable of N2-fixation and phosphate-solubilization [57]. Limonium species have antibacterial, antioxidant, free radical-scavenging, and antiviral properties.

A. linearis and Cyclopia spp. are South African indigenous herbal leguminous species grown in acidic soils. Among the rhizobial isolates from root nodules of A. 24spalathus and Cyclopia spp., bacterial species of genera Rhizobium, Burkholderia, Mesorhizobium, and Bradyrhizobium produce bioactive compounds that affect the growth of leguminous plants [58].

A heavy-metal-resistant strain of Bacillus edaphicus NBT was evaluated on B. juncea for its plant growth promotion. B. edaphicus NBT produced indole acetic acid, siderophores, and aminocyclopropane-1-carboxylic acid deaminase. There was also an increase in Pb uptake by B. juncea inoculated with B. edaphicus NBT [208]. In pot experiments, 16S rDNA sequencing identified E. aerogenes and R. aquatilis isolated from B. juncea. These isolates stimulated the growth of B. juncea exposed to environments contaminated with Ni and Cr [209]. These bacteria also produced siderophores, aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, and phosphate solubilization [209]. B. pumilus (STR2) and Exiguobacterium oxidotolerans (STR36) promoted the growth of the water hyssop (Bacopa monnieri (L.) Pennell) grown in salt-stressed soils, enhanced proline levels and decreased lipid peroxidation [76]. Traditional medicine from B. monnieri may improve cognitive performance, cure ADHD symptoms, and lessen stress and anxiety.

The jute mallow or nalta jute (Corchorus olitorius L.) inoculated with P. extremorientalis TSAU6, indole acetic acid, and gibberellic acid exhibited a significant increase in root length, shoot length, and fresh weight, indicating that plant growth regulators such as auxins and gibberellins play an important role in plant salinity tolerance [59]. C. olitorius is a leafy vegetable that is frequently used in soup recipes and traditional medicine to treat tumors, chronic cystitis, and fever. B. megaterium MTCC446 isolated from gale of the wind (Phyllanthus amarus Schumach. and Thonn.) promoted a higher vigor index, germination (%), plant biomass, P content, plant phenolic content, radical scavenging, and antioxidant activity [60]. P. amarus is frequently used in African traditional medicine to treat a variety of illnesses, including kidney stones, dysentery, jaundice, diarrhea, and urogenital problems.

Under the pot experiment, Achromobacter xylosoxidans isolated from the bright eyes (Catharanthus roseus (L.) G. Don) exposed to saline soils in Tamilnadu, India, produced aminocyclopropane-1-carboxylic acid deaminase [210]. C. roseus is a significant medicinal plant that is found around the world. It contains a variety of phytochemicals that have biological effects (antioxidant, antibacterial, antifungal, and anticancer). Under drought conditions, the ringed lavender (Lavandula dentata L.) isolates of B. thuringiensis increased plant growth and nutrition. B. thuringiensis produced indole acetic acid and aminocyclopropane-1-carboxylic acid deaminase and solubilized P, demonstrating its capacity to enhance plant growth under stress conditions [102]. In traditional medicine, L. dentata has been used to cure rheumatism, headaches, colds, and the flu.

Environmental contamination became a major challenge in recent decades due to rapid industrialization in developed countries. Mining activities, wastewater discharge, volcanic eruptions, and rock weathering affected the growth and productivity of soil. Endophytic bacterial species could be a potential mechanism in phytoremediation strategies for the management of environmental contaminants, while plants benefit through growth promotion (

Table 3. Phytoremediation bacteria and associated secondary metabolites from medicinal and herbal plant species.

Isolated Bacterial Species	Biochemical/Physiological Activity	Host Medicinal Plant Species	Isolated Plant Part/Region	References
Pseudomonas aeruginosa, Pseudomonas savastanoi	Mono- and dechlorinated, benzoic acids production	Elymus dauricus		[211]
Methylobacterium populi	Methane; 2,4,6-trinitrotoluene; hexahydro-1,3,5-trinitro-1,3,5-triazene; octahydro-1,3,5,7-tetranitro-1,3,5-tetrazocine; benzene, toluene, ethylbenzene, xylene production	Populus deltoids x nigra	NM	[212]
Pseudomonas sp., Bacillus cepacia	Benzene, toluene, ethylbenzene, xylene production	Populus sp.	NM	[213]
Burkholderia cepacia	Volatile organic compounds, toluene production	Lupinus luteus	NM	[214]
Pseudomonas putida	2,4-Dichlorophenoxyacetic acid production	Populus sp., Trichocarpa deltoides cv. Hoogvorst	Stem	[213]
Proteobacteria sp.	NM	Populus nigra cv. Brandaris	Root, shoot	[215]
Proteobacteria sp.	NM	Lolium multiflorum cv. Lolita	Root, shoot	[215]
Proteobacteria sp.	NM	Medicago sativa cv. Europ	Root, shoot	[215]
Pseudomonas! uorescens G10, Microbacterium sp. G16 (EN)	indole acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylate deaminase production	Brassica napus	Root	[216]
Arthrobacter sp. MT16, Microbacterium sp. JYC17, Pseudomonas chlororaphis SZY6	NM	Brassica napus	Whole plant	[217]
Firmicutes sp., Actinobacteria sp., Proteobacteria sp. (EN)	NM	Elsholtzia splendens, Commelina communis	Whole plant	[218]
Enterobacter sp.	NM	Allium macrostemon	Stem	[219]
Sphingopyxis sp., Pseudomonas sp.	NM	Lolium multiflorum, Lotus corniculatus	Root, shoot	[220]
Achromobacter xylosoxidans	NM	Phragmites australis, Ipomoea aquatica, Vetiveria zizanioides	Root	[221]
Burkholderia macroides	NM	Populus cv. Hoogvorst	Stem	[222]
Pseudomonas putida	NM	Populus trichocarpa × deltoides cv. Hoogvorst	Stem	[222]
Pseudomonas tolaasii, P. jessenii, Ps. Rhodesiae, P. plecoglossicida, P. veronii, P. fulva, P. oryzihabitans, Acinetobacter lwoffi, A. nicotianae, Bacillus megaterium, Paenibacillus amylolyticus	NM	Populus sp. cv. Hazendans	Root, stem	[15]
Pseudomonas putida	NM	Populus sp.	NM	[223]
Staphylococcus sp., Microbacterium sp., Pseudomonas sp., Staphylococcus sp., Curtobacterium sp., Microbacterium sp., Curtobacterium sp., Staphylococcus sp., Bacillus sp., Arthrobacter sp., Pseudomonas sp., Curtobacterium sp., Microbacterium sp., Paenibacillus sp., Leifsonia sp.	NM	Alyssum bertolonii	Leaf, stem, root	[224]
Bacillus sp.	NM	Alnus firma	Root	[225]
Sphingomonas sp., Methylobacterium sp., Sphingobacterium multivorum, Phyllobacterium sp., Devosia sp., Afibia sp., Sphingomonas sp., Rhodococcus sp.	NM	Thlaspi caerulescens	Stem, root	[226]
Alphaproteobacteria sp., Holophaga sp., Acidobacterium sp., Betaproteobacteria sp., Gammaproteobacteria sp., Bacillus sp., Blastococcus sp., Propionibacterium acnes, Flavobacterium sp., Desulfitobacterium metallireductans, M. mesophilicum, M. extorquens, Sphingomonas sp., Curtobacterium sp., Plantibacter flavus, Rhodococcus sp.	NM	Thlaspi goesingense	Stem	[227]
Microbacterium sp., Bacillus sp., Arthrobacter sp., Flavobacterium sp., Chryseobacterium sp., Agrobacterium sp., Sphingomonas sp., Pseudomonas sp., Serratia sp., Curtobacteriu sp.	NM	Solanum nigrum	Root, stem, leaf	[228]
Acinetobacter sp., Bacillus sp.	Aminocyclopropane-1-carboxylic acid deaminase production	Commelina communis	Root, stem, leaf	[229]
Acinetobacter sp., Moraxella sp., Serratias sp., Herbaspirillum sp., Bukholderia sp., Paracoccus sp., Sphingomonas sp., Exiguobacterium sp., Bacillus sp., Arthrobacter sp., Microbacterium sp., Micrococcus sp.	NM	Elsholtzia splendens and Commelina communis	Root, stem, leaf	[230]
Enterobacter sp.	NM	Allium macrostemon	Stem	[231]
Microbacterium sp., Frigoribacterium sp., Methylobacterium sp., Sphingomonas sp.	NM	Salix caprea	Stem, leaf	[232]
Pseudomonas frederisksbergensis sp. Veronii, P. Putida, Arthrobacter illicis, A. histidinolovorans	NM	Populus sp. cv. Hazendans and Populus sp. cv. Hoogvorst	Root, stem	[168]
Staphylococcus sp., Microbacterium sp., Pseudomonas sp., Curtobacterium sp., Bacillus sp., Arthrobacter sp., Paenibacillus sp., Leifsonia sp.	NM	A. bertolonii	Whole plant	[168]
Pseudomonas sp., Streptomyces sp.	NM	A. bertolonii	Rhizosphere	[168]
Holophaga sp., Acidobacterium sp., Gammaproteobacteria sp., Betaproteobacteria sp., Alphaproteobacteria sp., Verrucomicrobia sp., Gemmatimonadetes sp.	NM	Thlaspi goesingense	Rhizosphere, shoot	[168]
Pseudomonas fluorescens G10, Microbacterium sp. G16	Indole acetic acid, aminocyclopro-pane-1-carboxylic acid deaminase, siderophore production	Brassica napus	Root, shoot	[172]
Enterobactor cloacae CAL2	Indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase, siderophores, antibiotics production	B. napus	Root, shoot	[172]
Cupriavidus taiwanensis	Biodegradation, biosorption, release of extracellular products	Mimosa pudica	Root, shoot	[172]
Bacillus thuringiensis GDB-1	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, Siderophores	Alnus firma	Root, shoot	[172]
B. pumilus E2S2, Bacillus sp. E1S2	Indole acetic acid, aminocyclo-pro-pane-1-carboxylic acid deaminase, siderophores	Sedum plumbizincicola	Root, shoot	[172]
Pseudomonas tolaasii ACC23, P. fluorescens ACC9	Aminocyclo-pro-pane-1-carboxylic acid deaminase, siderophores, and indole acetic acid production	B. napus	Root, shoot	[172]
Pseudomonas sp. LK9	Biosurfactants, siderophores, organic acids production	Solanum nigrum	Root, stem, leaf	[172]
Pseudomonas sp. PsM6, P. Jessenii PjM15	Biosorption, mobilization, aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, siderophores production	Ricinus communis	Root, stem, leaf	[172]
Rahnella sp. JN6	Indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase, siderophores	B. napus	Root, shoot	[172]
Bacilus subtilis, B. cereus, Flavobacterium sp., Pseudomonas aeroginosa	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, siderophores	Orycoprhagmus violaceus	Root, shoot	[172]
Pseudomonas veronii	indole acetic acid production, decrease soil pH, supply P, and Fe	S. alfredii	Root, shoot	[172]
Staphylococcus arlettae NBRIEAG-6	indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	Root, shoot	[172]
Achromobacter xylosoxidans Ax10	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid production	B. Juncea	Root, shoot	[172]
Psychrobacter sp. SRA1, Bacillus cereus SRA10	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid, Ni mobilization	B. Juncea	Root, shoot	[172]
Pseudomonas sp. SRI2, Psychrobacter sp. SRS8, Bacillus sp. SN9	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid production; Ni mobilization	B. Juncea	Root, shoot	[172]
Pseudomonas sp. SRI2, Psychrobacter sp. SRS8, Bacillus sp. SN9	Aminocyclopropane-1-carboxylic acid deaminase, indole acetic acid production; Ni mobilization	Brassica oxyrrhina	Root, shoot	[172]
Paenibacillus macerans NBRFT5, Bacillus endophyticus NBRFT4, B. pumilus NBRFT9	Siderophores, organic acids, protons, and other non-specified enzymes production	B. Juncea	Root, stem, leaf	[172]
Rhizobium leguminozarum	Metal chelation	B. Juncea	Whole plant	[172]
Azotobacter chroococcum HKN-5, Bacillus megaterium HKP-1, Bacillus mucilaginosun HKK-1	indole acetic acid, gibberellins production	B. Juncea	Shoot	[172]
Pantoea agglomerans Jp3-3, Pseudomonas thivervalensis Y1-3-9	Indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production	B. napus	Root, shoot	[172]
Enterobacter sp. JYX7, Klebsiella sp. JYX10	Indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production	Polygonum pubescens	Root, shoot	[172]
Rahnella sp.	Indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Amaranthus hypochondriacus, A. mangostanus, Solanum nigrum	Root, shoot	[172]
Kluyvera sp.	Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Kluyver spp.	Aminocyclopropane-1-carboxylic acid deaminase, siderophores production	Brassica juncea	NM	[172]
Brevibacillus sp.	Decreased lead uptake; indole acetic acid production	Trifolium pratense	NM	[172]
Enterobacter cloacae CAL2	Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Microbacterium arabinogalactanolyticum	Increased nickel uptake	Alyssum murale	NM	[172]
Psuedomonas sp.	Increased biomass; indole acetic acid production	Brassica napus	NM	[172]
Variovorax paradoxus, Rhodoccus sp., Flavobacterium sp.	Increased root length; Indole acetic acid, siderophores, production Aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Pseudomonas fluorescens, P. putida	Increased seed germination and growth	Brassica napus	NM	[172]
P. putida UW4, P. putida HS-2	Increased biomass in the field; indole acetic acid, Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Sinorhizobium sp. Pb002	Increased plant survival and lead uptake; aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Azotobacter chroococcum HKN-5, B. megaterium HKP-1, B. mucilaginosus HKK-1	Increased biomass and metal bioavailability	Brassica juncea	NM	[172]
B. subtilis SJ-101	Increased nickel uptake; indole acetic acid production	Brassica juncea	NM	[172]
Pseudomonas sp. RJ10, Bacillus sp. RJ16	Increased biomass and metal uptake; indole acetic acid production	Brassica napus	NM	[172]
Mesorhizobium huakuii subsp. Rengei B3	Increased metal accumulation: bacterium expresses phytochelatin, and metallothionein	Astragalus sinicus	NM	[172]
Burkholderia cepacia	Increased biomass, metal uptake, and translocation of metal to shoots	Sedum alfredii	NM	[172]
P. putida ARB86	Increased biomass and chlorophyll content	Arabidopsis thaliana	NM	[172]
Enterobacter sp. NBRI K28	Increased metal uptake; indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
P. putida HS-2	Increased seed germination and biomass; siderophores, indole acetic acid, Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Bacillus sp. J119	Increased cadmium uptake, indole acetic acid, siderophores production; biosurfactant production	Brassica napus	NM	[172]
P. aeruginosa MKRh3	Decreased cadmium uptake; indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production	Vigna mungo	NM	[172]
Pseudomonas sp. 29C, Bacillus sp. 4C	Increased biomass; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production;	Brassica juncea	NM	[172]
Pseudomonas sp. M6, Pseudomonas jessenii M15	Increased biomass; indole acetic acid, Aminocyclopropane-1-carboxylic acid deaminase production	Ricinus communis	NM	[172]
Proteus vulgaris KNP3	Increased germination, biomass, and chlorophyll, and decreased metal uptake	Cajanus cajan	NM	[172]
Pseudomonas sp.	Increased biomass and decreased metal uptake; siderophores production	Cicer arietinum	NM	[172]
P. fluorescens G10, Microbacterium sp. G16	Increased biomass and metal uptake; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Bacillus edaphicus NBT	Increased biomass; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Flavobacterium sp.	Increased root length, biomass, metal uptake	Orychophragmus violaceus	NM	[172]
Achromobacter xylosoxidans Ax10	Increased root and shoot length and biomass; aminocyclopropane-1-carboxylic acid deaminase production; indole acetic acid production	Brassica juncea	NM	[172]
Enterobacter aerogenes, Rahnella aquatilis	Increased biomass and metal uptake; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Kluyvera sp.	Increased biomass; aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Kluyvera sp.	Increased biomass; aminocyclopropane-1-carboxylic acid deaminase, siderophores production	Brassica napus	NM	[172]
Microbacterium arabinogalactanolyticum	Increased Ni uptake	Alyssum murale	NM	[172]
P. fluorescens, P. putida	Increased seed germination and growth	Brassica napus	NM	[172]
P. putida UW4, P. putida HS-2	Indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
B. subtilis SJ-101	Increased Ni, indole acetic acid production	Brassica juncea	NM	[172]
Bradyrhizobium sp. RM8	Decreased Ni toxicity and uptake; indole acetic acid, siderophores, hydrogen cyanide, ammonia production	Vigna mungo	NM	[172]
Rhizobium sp. RP5	Decreased Ni, Zn uptake, and toxicity; indole acetic acid, siderophores production	Pisum sativum	NM	[172]
Enterobacter sp. NBRI K28	Increased Ni, Zn, Cr uptake; I indole acetic acid, siderophores, Aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
P. putida HS-2	Siderophores, indole acetic acid, Aminocyclopropane-1-carboxylic acid deaminase production	Brassica napus	NM	[172]
Pseudomonas sp. 29C, Bacillus sp. 4C	indole acetic acid, siderophores production, Aminocyclopropane-1-carboxylic acid deaminase	Brassica juncea	NM	[172]
Pseudomonas sp. M6, Pseudomonas jessenii M15	indole acetic acid, aminocyclopropane-1-carboxylic acid deaminase production	Ricinus communis	NM	[172]
Pseudomonas sp.	Decreased Ni uptake; siderophores production	Cicer arietinum	NM	[172]
Enterobacter erogenes, Rahnella aquatilis	Increased Ni, Cr uptake; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea	NM	[172]
Psychrobacter sp. SRA1 and SRA2, Bacillus cereus SRA10	Increased Ni bioavailability and uptake; indole acetic acid, siderophores, aminocyclopropane-1-carboxylic acid deaminase production	Brassica juncea, B. oxyrrhina	NM	[172]
Brachybacterium	Production of halotolerant properties	Salicornia brachiate r	Rhizosphere	[233]
Pseudomonas sp. SRI2, Psychrobacter sp. SRS8 and Bacillus sp. SN9	NM	Brassica juncea, B. oxyrrhina	NM	[172]

NM = not mentioned.

).

3. Conclusions

The sustainable production of medicinal and herbal plants has been one of the major challenges facing agriculture in recent years, with the ongoing over-utilization of chemicals to meet the population demands. To solve these problems, an environmentally friendly way forward focusing on the minimal usage of agrochemicals is require. Endophytic bacterial isolates could be a potential source of phytochemical compounds to enhance plant production. In addition, endophytic bacteria enable the plant species to resist abiotic stress conditions. Endophytic bacterial living in plant tissues produce plant growth-promoting compounds such as phytohormones; enzymes such as Aminocyclopropane-1-carboxylic acid deaminase, which reduce the levels of ethylene; organic acids aiding in P solubilization; and siderophores, cellulases, and chitinases inhibiting the phytopathogens growth. Sustainable agriculture provides a platform to medicinal and herbal plant producers from which to apply new agricultural techniques and biotechnologies to enhance plant growth by using bacterial isolates as biofertilizers. The modes of actions of several endophytic bacterial species have been well documented; they are recognised as plant growth promotion agents based on other biochemical and physiological attributes such as biological nitrogen fixation, phosphate solubilization, siderophore production, and the synthesis of PGP substances. In addition to improving plant nutrient availability and providing protection against varied abiotic and biotic stresses, endophytic bacteria play a pivotal role in enhancing medicinal and herbal plant productivity while simultaneously ensuring the sustainable maintenance of soil health.