Endophytic Bacillus subtilis P10 from Prunus cerasifera as a biocontrol agent against tomato Verticillium wilt

Endophytic bacteria serve key roles in the maintenance of plant health and growth. Few studies to date, however, have explored the antagonistic and plant growth-promoting (PGP) properties of Prunus cerasifera endophytes. To that end, we isolated endophytic bacteria from P. cerasifera tissue samples and used a dual culture plate assay to screen these microbes for antagonistic activity against Verticillium dahliae, Botryosphaeria dothidea, Fusarium oxysporum, F. graminearum, and F. moniliforme. Of the 36 strains of isolated bacteria, four (strains P1, P10, P16, and P20) exhibited antagonistic effects against all five model pathogens, and the P10 strain exhibited the strongest antagonistic to five pathogens. This P10 strain was then characterized in-depth via phenotypic assessments, physiological analyses, and 16s rDNA sequencing, revealing it to be a strain of Bacillus subtilis. Application of a P10 cell suspension (1×108 CFU/mL) significantly enhanced the seed germination and seedling growth of tomato in a greenhouse setting. This P10 strain further significantly suppressed tomato Verticillium wilt with much lower disease incidence and disease index scores being observed following P10 treatment relative to untreated plants in pot-based experiments. Tomato plants that had been treated with strain P10 also enhanced defense-related enzymes, peroxidase, superoxide dismutase, and catalase activity upon V. dahliae challenge relative to plants that had not been treated with this endophytic bacterium. The results revealed that the P10 bacterial strain has potential value as a biocontrol agent for use in the prevention of tomato Verticillium wilt.

The Employment of Endophytic Bacteria for Phytodegradation of Pyridine

Pyridine is considered a heterocyclic aromatic chemical that is poisonous and carcinogenic to a variety of living species. The use of plant and endophytic- bacteria to improve the efficiency of pollutants extraction is considered a viable technique since the endophytic bacteria help in the adaptation of the plant itself in various ecosystems and have significant ecological importance because they improve the soil fertility and quality. This research aims to stimulate the pyridine phytodegradation by Phragmites australis plants using the endophytic bacterial strain, Acinetobacter by inoculation these bacterial cells to the plants to see if it might increase plant growth and pyridine phytodegradation. In the present study, the system of pyridine phytodegradation basins with the vertical subsurface flow (VSSF) was adopted, since this system has better ventilation. In addition, the retention time is several hours due to the penetration of water molecules to the layers of packing materials of the basin, which have a relatively high hydraulic conductivity. After conducting the experiments, samples were collected and tests were done to find out the optimum conditions. The results were recorded as 40 plants of P. australis/m2 of VSSF systems; bacterial cells concentration, 250 mg/L; pyridine concentration, 400 mg/L; temperature, 35 °C and pH, 8±2 for 10 hrs incubation duration. As a result, endophytic bacteria can break down toxic organic substances in combination with certain plants. When the endophytic bacterium, Acinetobacter was not used to enhance the role of Phragmites australis plants in the pyridine-phytodegradation process, the rate of phytodegradation was reduced to less than 30% at a pyridine concentration of 700 mg/L, indicating the importance of this endophytic bacterium in the pyridine phytodegradation process.

Bacterial Endophytes as a Promising Approach to Enhance the Growth and Accumulation of Bioactive Metabolites of Three Species of Chenopodium Sprouts

Sprouts are regarded as an untapped source of bioactive components that display various biological properties. Endophytic bacterium inoculation can enhance plant chemical composition and improve its nutritional quality. Herein, six endophytes (Endo 1 to Endo 6) were isolated from Chenopodium plants and morphologically and biochemically identified. Then, the most active isolate Endo 2 (strain JSA11) was employed to enhance the growth and nutritive value of the sprouts of three Chenopodium species, i.e., C. ambrosoides, C. ficifolium, and C. botrys. Endo 2 (strain JSA11) induced photosynthesis and the mineral uptake, which can explain the high biomass accumulation. Endo 2 (strain JSA11) improved the nutritive values of the treated sprouts through bioactive metabolite (antioxidants, vitamins, unsaturated fatty acid, and essential amino acids) accumulation. These increases were correlated with increased amino acid levels and phenolic metabolism. Consequently, the antioxidant activity of the Endo 2 (strain JSA11)-treated Chenopodium sprouts was enhanced. Moreover, Endo 2 (strain JSA11) increased the antibacterial activity against several pathogenic bacteria and the anti-inflammatory activities as evidenced by the reduced activity of cyclooxygenase and lipoxygenase. Overall, the Endo 2 (strain JSA11) treatment is a successful technique to enhance the bioactive contents and biological properties of Chenopodium sprouts.

Plant Growth-Promoting Endophytic Bacillus Aryabhattai Triggers Novel Genes to Induce Plant Growth

Background: In nature, plants interact with a wide range of microorganisms. Most of these microorganisms have the ability to promote plant growth through the induction of important molecular pathways. The current work evaluated whether the endophytic bacterium Bacillus aryabhattai encourages plant growth and how transcriptional changes might be implicated in this effect.Results: The endophytic bacterium showed a significant effect on plant growth. Our results revealed that B. aryabhattai promotes the growth of Arabidopsis and tobacco plants. Notably, transcriptional changes in Arabidopsis plants treated with the bacterium were identified. Genes such as cinnamyl alcohol dehydrogenase, apyrase, thioredoxin H8, benzaldehyde dehydrogenase, indoleacetaldoxime dehydratase, berberine bridge enzyme-like and gibberellin-regulated protein were highly expressed. Additionally, endophytic bacterial genes such as arginine decarboxylase, D-hydantoinase, ATP synthase gamma chain and 2-hydroxyhexa-2,4-dienoate hydratase were activated during the interaction with Arabidopsis.Conclusions: The results show that new plant growth-related genes are induced during the interaction endophytic bacterium B. aryabhattai, and these changes may promote plant growth in sustainable agriculture.

Influence of Endophytic Bacterium, Cellulosimicrobium sp. FRR2 on Plant Growth of Amaranthus campestris L. and Bacterial Survival at Adverse Environmental Conditions

The endophytic microorganisms are believed to be an important bio-resource for modern agriculture because of their beneficial effects on plant growth promotion, biocontrol, stress tolerance, and diseases resistance. This study was focused to know the beneficial effect of endophytic bacterium (FRR2) isolated from the roots of Ficus religiosa L. on Amaranthus campestris L. and their tolerance ability against salinity and heavy metals. The strain FRR2 was recognized as Cellulosimicrobium sp. by 16s rRNA sequencing and phylogenetic study. The bacterial isolate FRR2 showed salt (at 150 mM NaCl) and metal (at 150 µM CuSO4 and 100 µM ZnSO4) tolerance ability and significantly higher growth rate of Amaranthus campestris in a green leafy vegetable might be due to the nitrogen fixation, indole acetic acid production, amylase and protease activities. In addition, the endophyte FRR2 application slightly increased the antioxidants activity than their controls. The results of this study revealed that Cellulosimicrobium sp. strain FRR2 would be an effective endophyte to increase the growth of green leafy vegetables.

Phenylalanine 4-Hydroxylase Contributes to Endophytic Bacterium Pseudomonas fluorescens’ Melatonin Biosynthesis

Melatonin acts both as an antioxidant and as a growth regulatory substance in plants. Pseudomonas fluorescens endophytic bacterium has been shown to produce melatonin and increase plant resistance to abiotic stressors through increasing endogenous melatonin. However, in bacteria, genes are still not known to be melatonin-related. Here, we reported that the bacterial phenylalanine 4-hydroxylase (PAH) may be involved in the 5-hydroxytryptophan (5-HTP) biosynthesis and further influenced the subsequent production of melatonin in P. fluorescens. The purified PAH protein of P. fluorescens not only hydroxylated phenylalanine but also exhibited l-tryptophan (l-Trp) hydroxylase activity by converting l-Trp to 5-HTP in vitro. However, bacterial PAH displayed lower activity and affinity for l-Trp than l-phenylalanine. Notably, the PAH deletion of P. fluorescens blocked melatonin production by causing a significant decline in 5-HTP levels and thus decreased the resistance to abiotic stress. Overall, this study revealed a possible role for bacterial PAH in controlling 5-HTP and melatonin biosynthesis in bacteria, and expanded the current knowledge of melatonin production in microorganisms.

Coordinated bacterial and plant sulfur metabolism in Enterobacter sp. SA187–induced plant salt stress tolerance

Enterobacter sp. SA187 is a root endophytic bacterium that maintains growth and yield of plants under abiotic stress conditions. In this work, we compared the metabolic wirings of Arabidopsis and SA187 in the free-living and endophytic interaction states. The interaction of SA187 with Arabidopsis induced massive changes in bacterial gene expression for chemotaxis, flagellar biosynthesis, quorum sensing, and biofilm formation. Besides modification of the bacterial carbon and energy metabolism, various nutrient and metabolite transporters and the entire sulfur pathway were up-regulated. Under salt stress, Arabidopsis resembled plants under sulfate starvation but not when colonized by SA187, which reprogramed the sulfur regulon of Arabidopsis. In accordance, salt hypersensitivity of multiple Arabidopsis sulfur metabolism mutants was partially or completely rescued by SA187 as much as by the addition of sulfate, L-cysteine, or L-methionine. Many components of the sulfur metabolism that are localized in the chloroplast were partially rescued by SA187. Finally, salt-induced accumulation of reactive oxygen species as well as the hypersensitivity of LSU mutants were suppressed by SA187. LSUs encode a central regulator linking sulfur metabolism to chloroplast superoxide dismutase activity. The coordinated regulation of the sulfur metabolic pathways in both the beneficial microorganism and the host plant is required for salt stress tolerance in Arabidopsis and might be a common mechanism utilized by different beneficial microbes to mitigate the harmful effects of different abiotic stresses on plants.

Organization, evolution and function of fengycin biosynthesis gene clusters in the Bacillus amyloliquefaciens group

The Bacillus velezensis strain PG12, belonging to the Bacillus amyloliquefaciens group, is an endophytic bacterium known for its antimicrobial activities against crop pathogens. However, our knowledge of the molecular basis underlying its biocontrol activity and the relatedness of different strains in the Bacillus amyloliquefaciens group is limited. Here, we sequenced and analyzed the genome of PG12 to test its taxonomic affiliation and identified genes involved in the biocontrol activity. The phylogenomic analysis results indicate that PG12 belongs to B. velezensis, a subgroup of the B. amyloliquefaciens group. By comparing the genomes of 22 strains in this group, we confirmed that it comprises three different phylogenetic lineages: B. amyloliquefaciens, B. velezensis and B. siamensis. Three secondary metabolism gene clusters related to the production of lipopeptides, namely fengycin, iturin and surfactin, were identified in the genomes of the B. amyloliquefaciens group. The core genome of B. velezensis is enriched in secondary metabolism genes compared with B. siamensis and B. amyloliquefaciens. Three of the five genes pertaining to the gene cluster responsible for fengycin biosynthesis (fenBCD) were found in B. velezensis and B. siamensis, but not in B. amyloliquefaciens. Phenotypic analysis showed that the ∆fenA mutant of PG12 displayed significantly decreased biofilm formation and swarming motility, which indicates that fengycin contributes to the colonization and pathogen control abilities of PG12. Our results also suggest that B. siamensis and B. velezensis have acquired the fenBCD genes from Paenibacillus spp. by horizontal gene transfer (HGT). Taken together, the results provide insights into the evolutionary pattern of the B. amyloliquefaciens group strains and will promote further researches on their taxonomy and functional genomics.