Bacterial Endophytes Research Articles

Biosurfactant from Nile Papyrus endophyte with potential antibiofilm activity against global clones of Acinetobacter baumannii.

Acinetobacter baumannii is a leading cause of biofilm-associated infections, particularly catheter-related bloodstream infections (CRBSIs) that are mostly recalcitrant to antimicrobial therapy. One approach to reducing the burden of CRBSIs is inhibiting biofilm formation on catheters. Owing to their prodigious microbial diversity, bacterial endophytes might be a valuable source of biosurfactants, which are known for their great capacity to disperse microbial biofilms. With this in mind, our study aimed to screen bacterial endophytes from plants growing on the banks of the River Nile for the production of powerful biosurfactants capable of reducing the ability of A. baumannii to form biofilms on central venous catheters (CVCs). This was tested on multidrug- and extensive drug-resistant (M/XDR) clinical isolates of A. baumannii that belong to high-risk global clones and on a standard strain of A. baumannii ATCC 19606. The drop collapse and oil dispersion assays were employed in screening the cell-free supernatants (CFS) of all endophytes for biosurfactant activity. Of the 44 bacterial endophytes recovered from 10 plants, the CFS of Bacillus amyloliquefaciens Cp24, isolated from Cyperus papyrus, showed the highest biosurfactant activity. The crude biosurfactant extract of Cp24 showed potent antibacterial activity with minimum inhibitory concentrations (MICs) ranging from 0.78 to 1.56 mg/ml. It also showed significant antibiofilm activity (p-value<0.01). Sub-MICs of the extract could reduce biofilm formation by up to 89.59%, while up to 87.3% of the preformed biofilms were eradicated by the MIC. A significant reduction in biofilm formation on CVCs impregnated with sub-MIC of the extract was demonstrated by CV assay and further confirmed by scanning electron microscopy. This was associated with three log10 reductions in adhered bacteria in the viable count assay. GC-MS analysis of the crude biosurfactant extract revealed the presence of several compounds, such as saturated, unsaturated, and epoxy fatty acids, cyclopeptides, and 3-Benzyl-hexahydro-pyrrolo [1, 2-a] pyrazine-1,4-dione, potentially implicated in the potent biosurfactant and antibiofilm activities. In the present study, we report the isolation of a B. amyloliquefaciens endophyte from the plant C. papyrus that produces a biosurfactant with potent antibiofilm activity against MDR/XDR global clones of A. baumannii. The impregnation of CVCs with the biosurfactant was demonstrated to reduce biofilms and, hence, proposed as a potential strategy for reducing CRBSIs.

Aloe Vera Extract Gel-Biosynthesized Selenium Nanoparticles Enhance Disease Resistance in Lettuce by Modulating the Metabolite Profile and Bacterial Endophytes Composition.

The use of nanotechnology to suppress crop diseases has attracted significant attention in agriculture. The present study investigated the antifungal mechanism by which aloe vera extract gel-biosynthesized (AVGE) selenium nanoparticles (Se NPs) suppressed Fusarium-induced wilt disease in lettuce (Lactuca sativa). AVGE Se NPs were synthesized by utilizing sodium selenite as a Se source and AVGE as a biocompatible capping and reducing agent. Over 21 d, 2.75% of total AVGE Se NPs was dissolved into Se ions, which was more than 8-fold greater than that of bare Se NPs (0.34%). Upon exposure to soil applied AVGE Se NPs at 50 mg/kg, fresh shoot biomass was significantly increased by 61.6 and 27.8% over the infected control and bare Se NPs, respectively. As compared to the infected control, the shoot levels of citrate, isocitrate, succinate, malate, and 2-oxo-glutarate were significantly upregulated by 0.5-3-fold as affected by both Se NPs. In addition, AVGE Se NPs significantly increased the shoot level of khelmarin D, a type of coumarin, by 4.40- and 0.71-fold over infected controls and bare Se NPs, respectively. Additionally, AVGE Se NPs showed greater upregulation of jasmonic acid and downregulation of abscisic acid content relative to bare Se NPs in diseased shoots. Moreover, the diversity of bacterial endophytes was significantly increased by AVGE Se NPs, with the values of Shannon index 40.2 and 9.16% greater over the infected control and bare Se NPs. Collectively, these findings highlight the significant potential of AVGE Se NPs as an effective and biocompatible strategy for nanoenabled sustainable crop protection.

Diversity and Biocontrol Potential of Endophytic Fungi and Bacteria Associated with Healthy Welsh Onion Leaves in Taiwan.

Foliar diseases caused by Stemphylium and Colletotrichum species are among the major biotic factors limiting Welsh onion production in Taiwan. Owing to concerns about the environment and the development of pathogen resistance to existing fungicides, biological control using endophytes is emerging as an eco-friendly alternative to chemical control. The aim of the present study was to isolate endophytes from healthy Welsh onion leaves and investigate their antagonistic potential against the major phytopathogenic fungi associated with Welsh onion plants in Taiwan. A total of 109 bacterial and 31 fungal strains were isolated from healthy Welsh onion leaves and assigned to 16 bacterial and nine fungal genera using morphological and molecular characterization based on DNA sequence data obtained from nuclear internal transcribed spacer (nrITS) (fungi) and 16S rRNA (bacteria). Evaluation of these endophytic isolates for biocontrol activity against leaf blight pathogens Colletotrichum spaethianum strain SX15-2 and Stemphylium vesicarium strain SX20-2 by dual culture assay and greenhouse experiments resulted in the identification of two bacterial isolates (GFB08 and LFB28) and two fungal isolates (GFF06 and GFF08) as promising antagonists to leaf blight pathogens. Among the four selected isolates, Bacillus strain GFB08 exhibited the highest disease control in the greenhouse study. Therefore, Bacillus strain GFB08 was further evaluated to understand the mechanism underlying its biocontrol efficacy. A phylogenetic analysis based on six genes identified Bacillus strain GFB08 as B. velezensis. The presence of antimicrobial peptide genes (baer, bamC, bmyB, dfnA, fenD, ituC, mlna, and srfAA) and the secretion of several cell wall degrading enzymes (CWDEs), including cellulase and protease, confirmed the antifungal nature of B. velezensis strain GFB08. Leaf blight disease suppression by preventive and curative assays indicated that B. velezensis strain GFB08 has preventive efficacy on C. spaethianum strain SX15-2 and both preventive and curative efficacy on S. vesicarium strain SX20-2. Overall, the current study revealed that healthy Welsh onion leaves harbour diverse bacterial and fungal endophytes, among which the endophytic bacterial strain, B. velezensis strain GFB08, could potentially be used as a biocontrol agent to manage the leaf blight diseases of Welsh onion in Taiwan.

Bacterial endophytes of sugar maple leaves vary more idiosyncratically than epiphytes across a large geographic area.

Bacteria from the leaf surface and the leaf tissue have been attributed with several beneficial properties for their plant host. Though physically connected, the microbial ecology of these compartments has mostly been studied separately such that we lack an integrated understanding of the processes shaping their assembly. We sampled leaf epiphytes and endophytes from the same individuals of sugar maple across the northern portion of its range to evaluate if their community composition was driven by similar processes within and across populations differing in plant traits and overall abiotic environment. Leaf compartment explained most of the variation in community diversity and composition across samples. Leaf epiphytic communities were driven more by host and site characteristics than endophytic communities, whose community composition was more idiosyncratic across samples. Our results suggest a greater importance of priority effects and opportunistic colonization in driving community assembly of leaf endophytes. Understanding the comparative assembly of bacterial communities at the surface and inside plant leaves may be particularly useful for leveraging their respective potential for improving the health of plants in natural and anthropized ecosystems.

Bacterial Endophytes from Moringa oleifera Leaves as a Promising Source for Bioactive Compounds

Bacterial endophytes reside within the tissues of living plant species without causing any harm or disease to their hosts. Bacterial endophytes have produced a variety of bioactive compounds that can be used for different biomedical applications. In the current study, two bacterial endophytes were isolated from healthy Moringa oleifera leaves, and identified genetically as Stenotrophomonas maltophilia and Alcaligenes faecalis. Phytochemical results illustrated that A. faecalis produced phenolics at 547.2 mg/g, tannins at 156.7 µg/g, flavonoids at 32.8 µg/g, and alkaloids at 111.2 µg/g compared to S. maltophilia, which produced phenolics at 299.5 mg/g, tannins at 78.2 µg/g, flavonoids at 12.4 µg/g, and alkaloids at 29.4 µg/g. GC-MS analysis indicated that A. faecalis extract has 24 bioactive compounds, including 9 major compounds, namely octadecanoic acid, hexadecanoic acid, linoleic acid ethyl ester, octadecenoic acid, methyl ester, methyl stearate, nonacosane, indolizine, palmitoleic acid, and heptacosane. On the other hand, S. maltophilia extract has 11 bioactive compounds, including 8 major compounds, namely oleic acid, octadecanoic acid, hexadecanoic acid, cis-2-phenyl-1, 3-dioxolane-4-methyl, ergotamine, diisooctyl phthalate, diethyl phthalate, and pentadecanoic acid. To check the safety of these extracts, the cytotoxicity of Ethyl acetate (EA) extracts of S. maltophilia and A. faecalis were evaluated against the Vero normal cell line, and the results confirmed that these extracts are safe to use. Moreover, results revealed that EA extracts of S. maltophilia and A. faecalis exhibited anticancer activity against the cancerous MCF7 cell line, where IC50 was 202.4 and 119.7 µg/mL, respectively. Furthermore, EA extracts of S. maltophilia had antibacterial and antifungal activity against Gram-positive and Gram-negative bacteria, and unicellular fungi. Likewise, the EA extract of A. faecalis exhibited antibacterial and antifungal activity against Gram-positive bacteria, as well as unicellular fungi, but did not show any activity against Gram-negative bacteria. Also, EA extracts of S. maltophilia and A. faecalis exhibited moderate antioxidant activity where IC50 were 146.2 and 147.6 µg/mL, respectively. In conclusion, the two isolated endophytic bacteria S. maltophilia and A. faecalis have promising bioactive compounds that have antibacterial, antioxidant, and anticancer activities.

Isolation and plant growth promoting properties of bacterial endophytes from wild plant (Wedelia urticifolia) of south Gujarat region

Isolation and plant growth promoting properties of bacterial endophytes from wild plant (Wedelia urticifolia) of south Gujarat region

PROMISING BIOFERTILISING ENDOPHYTES AS HUMAN PATHOGENS SUPPRESSOR AGENTS

Despite the very good consideration regarding organic products, studies have shown that leafy vegetables can harbour various human pathogens. Preventive methods are the best way to reduce such risks and protect the quality and image of organic agricultural production. The aim of this study was to suppress important human pathogens, bacteria, and yeasts, by using selected plant beneficial endophytes. Results have showed that among 23 bacterial endophytes isolated from different plant species, some isolates revealed antimicrobial activity. Reference strains of Bacillus cereus and methicillin-sensitive Staphylococcus aureus were inhibited by 34.8% of the isolated endophytes, while the methicillin-resistant strain of S. aureus was inhibited by 30.4% of the tested endophytes. Enterococcus faecalis and Salmonella typhimurium were more reticent, and only 8.7% of the isolated endophytes were able to inhibit their growth. The pathogenic reference yeasts, Candida albicans and C. parapsilosis were inhibited by 17.4% and 21.7%, respectively of the isolated endophytes. In vitro results revealed certain strains of endophytic bacteria as potential inoculants, to provide not only plant growth promotion but also protection against important pathogenic contaminants.

Bacterial Endophytes, a resilient way toward sustainable agriculture: provide plant growth promotion and biocontrol of plant pathogens

Plant pathogens are considered a major constraint in decreasing the quality and quantity of plants and plant products by attacking the seed from its germination to the harvesting stage. To date, various multifunctional chemical pesticides have been applied to control these infectious entities, but these chemical pesticides are not as effective in controlling them. That is why "bacterial endophytes," an alternative to these chemical pesticides, have been determined in the history of mankind through multidisciplinary ways. At the same time, these endophytes work to save the living environment, improve plant growth, and control infectious plant pathogens. The current study summarizes and analyzes the pioneering and recent works on plant bacterial endophytes and their mechanisms as biocontrol agents/plant growth promotion, interaction with the host plant, root colonization, systemic colonization of aerial plant tissues, phytohormone production and modulation, host specificity, genes expressed in the endosphere, multi-omics approaches to improve endophyte use, and biopesticide formulation by these bacterial endophytes. The manuscript highlights the most necessary information about bacterial endophytes, and the study will play a vital role in the further use and handling of these bacterial endophytes for sustainable agricultural production.

Endophytes Producing Proteases from Custard Apple (Annona squamosa L.) Leaves

The cost of the proteolytic enzymes and their inability to remove “fine” hairs from the animal hide has been the main obstacles to the commercialization of an enzymatic dehairing procedure. Endophytic microbes that grow inside various plant tissues without causing tissue damage in the host plant are the important sources of bioactive compounds. They are rich in secondary metabolites and known to produce wide range of enzymes. Several endophytes showing different properties have been reported from Annona leaves and hence this study was performed to isolate endophytes having proteolytic properties. Endophytes from custard apple leaves were isolated and screened for proteolytic activity on casein agar plates. The protease enzyme activity of the promising isolates was determined using casein substrate and tyrosine release assay. Present study conducted on the bacterial endophytes from the Custard apple leaves showed that the plant-associated bacterial endophytes are a good reservoir of proteases. Two promising isolates were obtained on the casein agar plates. These two isolates C and D possessed 113U/ml and 102 U/ml enzyme activity respectively. The isolate C showed more dehairing capacity than isolate D. Purified forms of these enzymes can prove to be potential candidates in biotechnological applications.

Characterization of endophytic bacteriome diversity and associated beneficial bacteria inhabiting a macrophyte Eichhornia crassipes.

The endosphere of a plant is an interface containing a thriving community of endobacteria that can affect plant growth and potential for bioremediation. Eichhornia crassipes is an aquatic macrophyte, adapted to estuarine and freshwater ecosystems, which harbors a diverse bacterial community. Despite this, we currently lack a predictive understanding of how E. crassipes taxonomically structure the endobacterial community assemblies across distinct habitats (root, stem, and leaf). In the present study, we assessed the endophytic bacteriome from different compartments using 16S rRNA gene sequencing analysis and verified the in vitro plant beneficial potential of isolated bacterial endophytes of E. crassipes. Plant compartments displayed a significant impact on the endobacterial community structures. Stem and leaf tissues were more selective, and the community exhibited a lower richness and diversity than root tissue. The taxonomic analysis of operational taxonomic units (OTUs) showed that the major phyla belonged to Proteobacteria and Actinobacteriota (> 80% in total). The most abundant genera in the sampled endosphere was Delftia in both stem and leaf samples. Members of the family Rhizobiaceae, such as in both stem and leaf samples. Members of the family Rhizobiaceae, such as Allorhizobium- Neorhizobium-Pararhizobium-Rhizobium were mainly associated with leaf tissue, whereas the genera Nannocystis and Nitrospira from the families Nannocystaceae and Nitrospiraceae, respectively, were statistically significantly associated with root tissue. Piscinibacter and Steroidobacter were putative keystone taxa of stem tissue. Most of the endophytic bacteria isolated from E. crassipes showed in vitro plant beneficial effects known to stimulate plant growth and induce plant resistance to stresses. This study provides new insights into the distribution and interaction of endobacteria across different compartments of E. crassipes Future study of endobacterial communities, using both culture-dependent and -independent techniques, will explore the mechanisms underlying the wide-spread adaptability of E. crassipesto various ecosystems and contribute to the development of efficient bacterial consortia for bioremediation and plant growth promotion.

Re-introduction of a bioactive bacterial endophyte back to its seaweed (Ulva sp.) host, influences the host’s microbiome

Ulva is a commercially important marine macroalga. It hosts both epiphytes and endophytes. The latter are assumed to protect Ulva through secondary metabolites. Previously, we demonstrated bioactive endophytes from macroalgae with great potential to control diseases of aquaculture. In this study, we introduced a bioactive bacterial endophyte back into its original host (Ulva sp.) and demonstrated its survival over time in fresh and freeze-dried Ulva sp. We visualized the endophyte’s location and survival in the seaweed using a Green Fluorescent Protein (GFP) reporter gene. The isolate colonized the intercellular space and survived for at least 5 months in fresh, and 12 months in freeze-dried algae, while maintaining its bioactivity against the aquaculture pathogen Streptococcus iniae. We studied the influence of the endophyte on the bacterial community in the Ulva sp. We found that once introduced, the endophyte significantly changed algal microbiota diversity and abundance. Two of Ulva’s associated bacterial species were quantified over time, suggesting different trends in absolute abundance of these bacteria between treatments. To the best of our knowledge, this is the first report of the successful introduction of an endophytic microorganism into macroalgal tissue. These findings may be useful in applied research for the potential management of aquaculture diseases.

Rhizosphere Soil Bacterial Communities and Bacterial Root Endophytes in Cotton farming is Influence by Cultivation of Transgenic Bt and non-Bt Cotton Crop Varieties

Rhizosphere Soil Bacterial Communities and Bacterial Root Endophytes in Cotton farming is Influence by Cultivation of Transgenic Bt and non-Bt Cotton Crop Varieties

Endophytes and Plant Extracts as Potential Antimicrobial Agents against Candidatus Liberibacter Asiaticus, Causal Agent of Huanglongbing.

Huanglongbing (HLB), also known as citrus greening, is an insidious disease in citrus and has become a threat to the sustainability of the citrus industry worldwide. In the U.S., Candidatus Liberibacter asiaticus (CLas) is the pathogen that is associated with HLB, an unculturable, phloem-limited bacteria, vectored by the Asian Citrus Psyllid (ACP, Diaphorina citri). There is no known cure nor treatment to effectively control HLB, and current control methods are primarily based on the use of insecticides and antibiotics, where effectiveness is limited and may have negative impacts on beneficial and non-target organisms. Thus, there is an urgent need for the development of effective and sustainable treatment options to reduce or eliminate CLas from infected trees. In the present study, we screened citrus-derived endophytes, their cell-free culture supernatants (CFCS), and crude plant extracts for antimicrobial activity against two culturable surrogates of CLas, Sinorhizobium meliloti and Liberibacter crescens. Candidates considered high-potential antimicrobial agents were assessed directly against CLas in vitro, using a propidium monoazide-based assay. As compared to the negative controls, statistically significant reductions of viable CLas cells were observed for each of the five bacterial CFCS. Subsequent 16S rRNA gene sequencing revealed that each of the five bacterial isolates were most closely related to Bacillus amyloliquefaciens, a species dominating the market of biological control products. As such, the aboveground endosphere of asymptomatic survivor citrus trees, grown in an organic orchard, were found to host bacterial endophytes capable of effectively disrupting CLas cell membranes. These results concur with the theory that native members of the citrus microbiome play a role in the development of HLB. Here, we identify five strains of Bacillus amyloliquefaciens demonstrating notable potential to be used as sources of novel antimicrobials for the sustainable management of HLB.

EXPLORING THE BIOEFFICACY OF ENDOPHYTIC BACTERIA AGAINST IMPORTANT PLANT PATHOGENS

The biological management of plant diseases has developed into a separate scientific and technological discipline, and in recent years, this change has happened quickly. A form of bacterium known as a bacterial endophyte may colonize any portion of a plant without causing any symptoms or harm to the host plant. Endophytic bacteria have been discovered by several researchers, and there is growing evidence that they can stop a variety of plant diseases from growing and functioning. Endophytes have a variety of benefits including growth-increasing and disease-hampering properties. Researchers’ interest in this field is growing as a result of its potentially to be utilized as an alternative to synthetic fungicides. This review's main objectives are to chart the development of endophytic bacterial research and give scientists access to current knowledge that will spur further investigation. Endophytic bacteria are employed to control plant diseases including wilt, rot and post-harvest damage, as well as nematode infestation. Endophytic bacteria are also used to control nematodes and postharvest diseases. With an emphasis on endophytic bacteria, this review explains the diverse mechanisms of bacterial endophytes to shield the plant from biotic infection.

Draft Genome Sequence of the Bacterial Endophyte Priestia megaterium B1, Isolated from Roots of Apple (Malus domestica).

Over the past years, a number of important traits supporting plant growth have been shown for different strains of Priestia megaterium (formerly known as Bacillus megaterium). Here, we report the draft genome sequence of the endophytic bacterial strain Priestia megaterium B1, which was isolated from surface-sterilized roots of apple plants.

Culturable bacterial endophytes of Aconitum carmichaelii Debx. were diverse in phylogeny, plant growth promotion, and antifungal potential.

Medicinal plants harbor tremendously diverse bacterial endophytes that maintain plant growth and health. In the present study, a total of 124 culturable bacterial endophytes were isolated from healthy Aconitum carmichaelii Debx. plants. These strains were clustered into 10 genera based on full-length 16S rDNA sequences, among which Bacillus and Pseudomonas were the dominant genera. In addition, A. carmichaelii may capture 10 potential new bacterial species based on multi-locus sequence analysis of three housekeeping genes (gyrA, rpoB, and atpD). The majority of these bacterial endophytes exhibited plant growth-promoting ability through diverse actions including the production of either indole acetic acid and siderophore or hydrolytic enzymes (glucanase, cellulose, and protease) and solubilization of phosphate or potassium. A total of 20 strains inhibited hyphal growth of fungal pathogens Sclerotium rolfsii and Fusarium oxysporum in vitro on root slices of A. carmichaelii by the dual-culture method, among which Pseudomonas sp. SWUSTb-19 showed the best antagonistic activity. Field experiment confirmed that Pseudomonas sp. SWUSTb-19 significantly reduced the occurrence of southern blight and promoted plant biomass compared with non-inoculation treatment. The possible mode of actions for Pseudomonas sp. SWUSTb-19 to antagonize against S. rolfsii involved the production of glucanase, siderophore, lipopeptides, and antimicrobial volatile compounds. Altogether, this study revealed that A. carmichaelii harbored diverse plant growth-promoting bacterial endophytes, and Pseudomonas sp. SWUSTb-19 could be served as a potential biocontrol agent against southern blight.

Isolation of endophytic bacteria from bryophytes and study of their morphological, biochemical and biofilm formation properties

Aim: To isolate an endophytic bacterial community associated with bryophytes, which were collected from various locations in Mount Abu, Rajasthan, and to characterise their morphological, biochemical, and biofilm development properties. Methodology: Different bryophytes were selected from various regions of Mount Abu, Rajasthan. On an R2A agar plate, colonies with various morphologies were isolated. Biofilm development of bacterial isolates was done on a glass surface and visualised through scaning electron microscopy. Biochemical test, such as indole test, catalase test, urease test, MR and VP tests, citrate utilization test, gelatine and nitrate test, etc., were determined as per Berge’s Manual of Determinative Bacteriology for characterization of endophytic bacteria. Salkowski's technique was also used for estimating IAA production by endophytic bacteria. Results: The results confirmed that isolates belonged to two phyla groups, Firmicutes and γ-proteobacteria with predomination of Firmicutes. Scanning electron microscopy showed that among all the isolates, rod-shaped bacteria dominated. The metabolic properties of endophytic bacteria showed that most bacterial isolates metabolised glucose, maltose and sucrose, however, only few bacterial endophytes metabolized lactose. Some isolates produced IAA growth hormones, which were analysed through Salkowski's technique. Interpretation: The findings indicate that bryophytes have associated bacterial diversity. The morphological and biochemical characterization of bacteria revealed that they are members of the Firmicutes and γ-proteobacteria phyla. SEM confirmed that bacterial isolates can form biofilm on glass surfaces and produce a distinct amount of IAA in a tryptophan-supplemented medium, essential for the growth and development of bryophytes. Key words: Bryophytes, Biofilm, Endophytic bacteria

Insight into Andrographis paniculata associated bacterial endomicrobiome and assessment of culturable bacterial endophytes for enhancement of industrially important andrographolide content

Andrographis paniculata is a common medicinal plant used worldwide for its preventive and curative properties. However, no information exists about the A. paniculata associated bacterial endophytes and their potential relationship with the plant-bioactive substances. In this study, we investigated the bacterial endophytic diversity of A. paniculata root and shoot tissues using culture-based and culture-independent high-throughput sequencing methods. The culture-independent analyses unveiled the presence of 465 operational taxonomic units (OTU’s) and 232 genera, respectively in the samples. Further, downstream categorization of OTU's revealed the dominance of Proteobacteria, Firmicutes, Actinobacteria and Bacteriodetes phylum members, with Bacillus being the most prevalent endophytic genera in the root, while Pseudomonas dominated the shoot tissues. A total of 39 bacterial endophytes from the roots, stems, leaves, and seeds of A. paniculata were isolated by a culture-dependent investigation whose subsequent examination using 16S rRNA gene sequencing confirmed a similar pattern of the dominance of the Bacillus and Pseudomonas genera. When all the isolates were further screened for their plant growth promotion activity, Micrococcus luteus (ASd6) significantly enhanced the biomass and andrographolide content by 68.01% and 44.16%, respectively. Taken together, the information captured through metagenomics and culture-dependent approach reveals some promising bacterial endophytes which could be employed in field for growth promotion and in planta secondary metabolite enhancement studies in near future.

Biocontrol Impacts on Wheat Physiology and Fusarium Head Blight Outcomes Are Bacterial Endophyte Strain and Cultivar Specific

Fusarium head blight (FHB) is an economically important disease of small grains globally and is primarily caused by Fusarium graminearum in North America. Recently, microbial biocontrols have risen in importance as sustainable agents of disease control. However, the path to implementation of microbial biocontrols in agriculture will require an understanding of how microbiota both affect plant performance overall and vary with inherent host disease resistance. Using a full-factorial, controlled greenhouse experiment, we tested how seven bacterial endophyte seed soak treatments affected both plant physiology prior to pathogen infection and FHB disease progression in Triticum aestivum (wheat). Bacterial endophyte treatments strongly affected the light-dependent reactions of photosynthesis, with changes in plant traits regulating light energy allocation and the build-up of electrochemical energy storage across the thylakoid membrane. Physiological responses were contingent on host variety. The direct effects of bacterial endophytes on wheat response to infection were weak and dependent on the inherent disease resistance of the host variety. However, disease outcomes were indirectly mediated by bacterial impacts on plant traits, with proton motive force traits emerging as common predictors of disease response across both host varieties and other traits indicating potential trade-offs in host response to bacterial inoculants and F. graminearum infection. Our results provide an alternate mechanism for microbial biocontrol efficacy other than direct antagonism with the pathogen inside the host. Furthermore, the chlorophyll-fluorescence and absorbance-based markers assessed here may have translational potential as a phenotyping tool for FHB susceptibility in wheat and other small grains.

Identification, Characterization, and Growth-Promoting Effects of Bacterial Endophytes Isolated from Okra (Abelmoschus esculentus L.)

Microorganisms colonize plant roots and exhibit plant growth promotion properties, therefore functioning as biofertilizers. To effectively use plant growth-promoting rhizobacteria, understanding their colonizing behavior and ability to compete with co-existing bacteria is essential. In this study, 12 endophytic bacterial strains belonging to seven genera in four classes with 99–100% homology were isolated from the roots of okra plants (Abelmoschus esculentus L.). Four isolates (Okhm3, Okhm5-4, Okhm10, and Okhm11) were inoculated on okra seeds and their effects on plant growth and colonization with single and mixed inoculations were evaluated. Okra was cultivated using sterilized vermiculite, and the growth parameters and colonization were measured 30 d after seed inoculation. All strains exhibited plant growth promotion traits that could improve okra plant growth in pot culture experiments. Notably, Okhm5-4 and Okhm10 strains (belonging to the Ensifer and Pseudomonas genera) revealed the highest growth-promoting effects on okra plants. Both strains were detected in the endosphere and rhizosphere of okra plants. Okhm10 and Okhm5-4, with lower colonization than Okhm3, showed better growth than Okhm3. Therefore, the colonization potential does not determine the growth-promoting effects. While Okhm3 populations remained stable in both inoculation conditions, the population level of other strains decreased in the mixed inoculation. This study showed bacterial endophytes isolated from Okra can be exploited as bio-fertilizers for sustainable agriculture systems.