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.

Keratinase Production by Endophytic Bacteria Aneurinibacillus aneurinilyticus VRCS-4 Isolated from Xerophytic Plant Opuntia ficus - indica (Prickly pear)

Bacterial endophytes colonize an ecological niche which is unexplored site makes them suitable to produce pharmacologically active substances with vast biotechnological potential therefore, xerophytes were chosen to isolate the endophytes. In the present study forty endophytic bacterial isolates were isolated from xerophytic plants grown near poultry farms and feather dumping sites. Of them eight isolates showed zone of hydrolysis and the maximum zone of hydrolyisis of 36mm was with VRCS-4 on skimmed milk agar. This isolate exhibited efficient feather degradation and was identified as Aneurinibacillus aneurinilyticus based on its morphological, biochemical test and molecular sequencing method. The isolate was deposited in NCBI with an accession number MW227423.The isolate showed maximum en-zyme activity of 140.24U/ml at 72h, pH 7.5 and 40º C at 140 rpm. Chicken feather 1% (w/v) used as a sole source of carbon and nitrogen. Feather deg-radation by A.aneurinilyticus VRCS-4 showed 90% degradation in feather meal broth. Ours appears to be the first report on keratinase production by endophytic bacteria from xerophytic plant (Opuntia ficus -indica).

Exploring Potential of Seed Endophytic Bacteria for Enhancing Drought Stress Resilience in Maize (Zea mays L.)

Water scarcity is abiotic stress that is becoming more prevalent as a result of human activities, posing a threat to agriculture and food security. Recently, endophytic bacteria have been proven to reduce drought stress and increase crop productivity. Here, we explored the efficacy of seed endophytic bacteria in maize crops under water deficit conditions. For this purpose, twenty-seven endophytic bacteria have been isolated from three distinct maize cultivars seeds (Malka 2016, Sahiwal Gold and Gohar-19) and evaluated for desiccation tolerance of −0.18, −0.491, and −1.025 MPa induced by polyethylene glycol (PEG) 6000. The nine isolates were chosen on the basis of desiccation tolerance and evaluated for maize growth promotion and antioxidant activity under normal and drought conditions. Results showed that drought stress significantly decreased the growth of maize seedlings. However, isolates SM1, SM4, SM19, and SM23 significantly improved the root and shoot length, plant biomass, leaf area, proline content, sugar, and protein content under normal and drought conditions. Antioxidant enzymes were significantly decreased at p-value < 0.05 with inoculation of seed endophytic bacteria under drought conditions. However, further experiments of seed endophytic bacteria (SM1, SM4, SM19, and SM23) should be conducted to validate results.

Analysis of Endophytic Bacterial Diversity From Different Dendrobium Stems and Discovery of an Endophyte Produced Dendrobine-Type Sesquiterpenoid Alkaloids

As the unique component of Dendrobium, dendrobine-type sesquiterpenoid alkaloids (DSAs) possess a variety of medicinal properties. It has been well documented that plant endophytes can in vitro synthesize secondary metabolites identical or similar to metabolites produced by their host plants. This study aimed to investigate the composition and distribution of endophytic bacteria of Dendrobium stems by Illumina MiSeq platform sequencing and cultivation-dependent methods and then to assess the potential for endophytic bacteria to produce DSAs. Results indicated that it was necessary to combine both cultivation-dependent and cultivation-independent methods to analyze the community structure of endophytic bacterial in plants comprehensively. The length of the Dendrobium stems influenced the endophytic bacterial community. The diversity and richness of endophytic bacteria in group J10_15cm of stems were the highest, which showed a significant difference from the other stem groups. However, there was no certain connection between the diversity and richness of endophytic bacteria and the content of dendrobine. It was most likely due to the influence of several specific endophytic bacteria genera, such as Sphingomonas and Rhodococcus. Athelia rolfsii, Myrothecium roridum, as pathogenic fungi, and Pectobacterium carotovorum subsp. actinidiae, as pathogenic bacteria of Dendrobium, were used to determine the antimicrobial activities. In these assays, six strains belonging to five genera showed antimicrobial activity against at least two phytopathogens. The strain BL-YJ10_15-29 (Paracoccus pueri THG-N2.35, 98.98%) showed the best antimicrobial activity against the three phytopathogens. In addition, 2 DSAs (6-hydroxydendrobine and nobilonine) were identified in the fermentation supernatant of the strain CM-YJ10_15-44 (Pseudomonas protegens CHA0, 99.24%), whereas the whole-genome analysis results further demonstrated that the precursors of the two DSAs [geranyl-PP and (E, E)-famesyl-PP] were synthesized mainly through the methyl-D-erythritol 4-phosphate pathway in this strain. This study provides new insight into the studies on the biosynthesis of DSAs and provides potential biocontrol bacteria.

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.

Plant growth‐promoting activity of endophytic bacteria from sweet sorghum (Sorghum bicolor (L.) Moench)

Application of high levels of chemical fertilizers for optimal growth of sweet sorghum causes environmental degradation. Plant growth‐promoting bacteria have biotechnological importance because they can improve the growth and health of important agronomic plants. This study aimed to isolate, characterize, and identify endophytic bacteria associated with sweet sorghum (cv. KCS105), and also to study the inoculation effects of selected isolates on sorghum growth. In this study, 35 isolates were evaluated for their ability to support plant growth. The results showed that seven isolates were diazotrophic, six were capable of dissolving phosphate, six produced IAA and could detect ACC‐deaminase activity, and three inhibited the growth of pathogenic fungi. Nine isolates exhibiting mechanisms for promoting plant growth from the Alphaproteobacteria (Devosia), Firmicutes (Bacillus, Paenibacillus, Staphylococcus), and Actinobacteria (Microbacterium, Brachybacterium) phyla were identified. In addition, the Paenibacillus sp. BB7, Bacillus sp. PIB1B, and Bacillus sp. PLB1B isolates showed increasing effects on plant growth in greenhouse tests. Endophytic bacterial isolates which display plant growth‐promoting features can potentially be employed as biofertilizer agents. They may also address environmental damage problems resulting from the use of chemical fertilizers and pesticides.

Plant growth promoting potential of multifarious endophytic Pseudomonas lini strain isolated from Cicer arietinum L.

Chickpea (Cicer arietinum), one of the major pulse crops in India, endured extreme reduction in production due to various abiotic and biotic stresses. Endophytic bacteria residing in the nodules and roots of chickpea plants enable host in combating these stresses. Twenty one endophytic bacteria isolated from nodules and roots of chickpea were screened for multiple plant growth promoting traits like ammonia, organic acid, siderophore, hydrogen cyanide (HCN) and phytohormone indole acetic acid (IAA) production. Out of these, 86% isolates produced ammonia, around 50% isolates produced organic acid, HCN and siderophore, 29% isolates produced ACC (1-aminocyclopropane-1-carboxylic acid) deaminase, while only 14% isolates solubilized phosphate. Interestingly, all the isolates were able to produce IAA ranging from 11.6–85.2 μg/ml, isolate CPJN 13 being the maximum IAA producer (85.5±2.33 μg/ml). Isolate CPJN13 was selected for IAA optimization studies. The yield of IAA increased up to 4 fold i.e. 331±4.96 μg/ml at optimized conditions. IAA production was also confirmed by TLC and HPLC analysis of crude IAA extract. The application of CPJN13 on chickpea seedlings resulted in significant increase in plant growth parameters. The 16S rDNA sequencing of CPJN13 revealed its similarity with Pseudomonas lini strain and submitted to NCBI with accession number MF574502. To best of our knowledge, this is the first report of the presence of P. lini as endophyte in chickpea nodules. The results of this study imply that the endophytic P. lini has a potential role to enhance the plant growth.