Peribacillus frigoritolerans T7-IITJ, a potential biofertilizer, induces plant growth-promoting genes of Arabidopsis thaliana.

AIMS: This study aimed to isolate plant growth and drought tolerance-promoting bacteria from the nutrient-poor rhizosphere soil of Thar desert plants and unravel their molecular mechanisms of plant growth promotion. METHODS AND RESULTS: Among our rhizobacterial isolates, Enterobacter cloacae C1P-IITJ, Kalamiella piersonii J4-IITJ, and Peribacillus frigoritolerans T7-IITJ, significantly enhanced root and shoot growth (4-5-fold) in Arabidopsis thaliana under PEG-induced drought stress. Whole genome sequencing and biochemical analyses of the non-pathogenic bacterium T7-IITJ revealed its plant growth-promoting traits, viz., solubilization of phosphate (40-73 µg/ml), iron (24 ± 0.58 mm halo on chrome azurol S media), and nitrate (1.58 ± 0.01 µg/ml nitrite), along with production of exopolysaccharides (125 ± 20 µg/ml) and auxin-like compounds (42.6 ± 0.05 µg/ml). Transcriptome analysis of A. thaliana inoculated with T7-IITJ and exposure to drought revealed the induction of 445 plant genes (log2fold-change > 1, FDR < 0.05) for photosynthesis, auxin and jasmonate signalling, nutrient uptake, redox homeostasis, and secondary metabolite biosynthesis pathways related to beneficial bacteria-plant interaction, but repression of 503 genes (log2fold-change < -1) including many stress-responsive genes. T7-IITJ enhanced proline 2.5-fold, chlorophyll 2.5-2.8-fold, iron 2-fold, phosphate 1.6-fold, and nitrogen 4-fold, and reduced reactive oxygen species 2-4.7-fold in plant tissues under drought. T7-IITJ also improved the germination and seedling growth of Tephrosia purpurea, Triticum aestivum, and Setaria italica under drought and inhibited the growth of two plant pathogenic fungi, Fusarium oxysporum, and Rhizoctonia solani. CONCLUSIONS: P. frigoritolerans T7-IITJ is a potent biofertilizer that regulates plant genes to promote growth and drought tolerance.

Isolation and Characterization of Stress-Tolerant Priestia Species from Cowpea Rhizosphere Under Drought and Nutrient Deficit Conditions.

This study aimed to isolate stress-tolerant phytobeneficial bacteria as bio-inoculants for cowpea's sustainable growth under drought and nutrient deficiency conditions. However, the application successful of phytobeneficial bacteria is subject to effective in vitro screening under different physiological conditions. We isolated several Priestia species from cowpea rhizosphere that tolerates polyethylene glycol (PEG6000)-induced drought and nutrient deficiency. Of them, C8 (Priestia filamentosa; basonym: Bacillus filamentosus), followed by C29 (Priestia aryabhattai; basonym: Bacillus aryabhattai), tolerated up to 20% PEG in a low-nutrient medium. In the presence of PEG, Priestia filamentosa and Bacillus aryabhattai exhibited optimal growth in different temperatures and pH but failed to survive at extreme temperatures of 45 °C and pH 11. Priestia filamentosa preferred L-proline and L-glutamate, while L-tryptophan and L-tyrosine were the least utilized. Interestingly, Priestia filamentosa and Bacillus aryabhattai used more complex nitrogen sources, peptone, and yeast extract, than inorganic nitrogen for growth. Most importantly, under drought and nutrient deficiency, Priestia filamentosa exhibited multiple plant growth-promoting traits and more amylase and protease production than C29. Our results indicate that Priestia filamentosa is a potential bacterium to enhance the growth of cowpea plants under stressful conditions.

Rhizosphere Priestia species altered cowpea root transcriptome and enhanced growth under drought and nutrient deficiency.

MAIN CONCLUSION: Priestia species isolated from the cowpea rhizosphere altered the transcriptome of cowpea roots by colonization and enhanced nutrient uptake, antioxidant mechanisms, and photosynthesis, protecting cowpea from drought and nutrient deficiency. Cowpea is a significant grain legume crop primarily grown in sub-Saharan Africa, Asia, and South America. Drought and nutrient deficiency affect the growth and yield of cowpea. To address this challenge, we studied the phyto-beneficial effects of stress-tolerant rhizobacteria on the biomass yield of cowpea under water- and nutrient-deficit conditions. Among the bacteria isolated, two rhizobacillus genotypes, C8 (Priestia filamentosa; basonym: Bacillus filamentosus) and C29 (Priestia aryabhattai; basonym: Bacillus aryabhattai) were evaluated for the improvement of seed germination and growth of cowpea under stress. Our study revealed that C8 protected cowpea from stress by facilitating phosphorus and potassium uptake, protecting it from oxidative damage, reducing transpiration, and enhancing CO2 assimilation. A 17% increase in root biomass upon C8 inoculation was concomitant with the induction of stress tolerance genes in cowpea roots predominantly involved in growth and metabolic processes, cell wall organization, ion homeostasis, and cellular responses to phosphate starvation. Our results indicate a metabolic alteration in cowpea root triggered by P. filamentosa, leading to efficient nutrient reallocation in the host plant. We propose inoculation with P. filamentosa as an effective strategy for improving the yield of cowpea in low-input agriculture, where chemical fertilization and irrigation are less accessible to resource-poor farmers.

Bacillus aryabhattai enhanced proline content, stabilized membrane and improved growth of cowpea under NaCl-induced salinity stress.

AIMS: Salinity stress affects the growth of cowpea particularly at the stages of seed germination and early vegetative growth. This study examined the potential of particular stress-tolerant rhizospheric bacteria to improve the growth of cowpea under conditions of salinity stress. METHODS AND RESULTS: Two rhizobacillus genotypes, Bacillus filamentosus-C8 and Bacillus aryabhattai-C29 were evaluated for their potentials to protect cowpea under NaCl-induced salinity stress. At 200 mM of NaCl concentration, control (non-inoculated) cowpea was affected, C8 was not able to significantly (p ≤ 0.05) alleviate the effects of salinity stress on cowpea growth while C29 significantly (p ≤ 0.05) reduced leaf wilting, increased chlorophyll content and improved the growth of cowpea plant under stressed condition. Interestingly, C29 significantly (p ≤ 0.05) induced high proline content and stabilized membrane by loss of electrolytes. CONCLUSION: Our results indicate that stabilized membrane and enhanced proline content by Bacillus aryabhattai-C29 supported the growth of cowpea under salinity stress condition. SIGNIFICANCE AND IMPACT OF THE STUDY: This study revealed that rhizospheric bacteria screened for salinity stress tolerant have potential to be used as an effective bioprotectant for sustainable growth of cowpea under salinity stress condition.

Biocementation mediated by native microbes from Brahmaputra riverbank for mitigation of soil erodibility.

Riverbank erosion is a global problem with significant socio-economic impacts. Microbially induced calcite precipitation (MICP) has recently emerged as a promising technology for improving the mechanical properties of soils. The present study investigates the potential of selectively enriched native calcifying bacterial community and its supplementation into the riverbank soil of the Brahmaputra river for reducing the erodibility of the soil. The ureolytic and calcium carbonate cementation abilities of the enriched cultures were investigated with reference to the standard calcifying culture of Sporosarcina pasteurii (ATCC 11859). 16S rRNA analysis revealed Firmicutes to be the most predominant calcifying class with Sporosarcina pasteurii and Pseudogracilibacillus auburnensis as the prevalent strains. The morphological and mineralogical characterization of carbonate crystals confirmed the calcite precipitation potential of these communities. The erodibility of soil treated with native calcifying communities was examined via needle penetration and lab-scale hydraulic flume test. We found a substantial reduction in soil erosion in the biocemented sample with a calcite content of 7.3% and needle penetration index of 16 N/mm. We report the cementation potential of biostimulated ureolytic cultures for minimum intervention to riparian biodiversity for an environmentally conscious alternative to current erosion mitigation practices.

Evaluation of therapeutic potentials of plant extracts against poultry bacteria threatening public health.

BACKGROUND: Plant extracts were evaluated on poultry bacteria known to be threatening public health. This is to develop better bio-therapeutic agents from plant origin. METHODS: Bacteria were isolated from water, feed, crop, gizzard and faeces of layer chicken. Isolates of interest (Escherichia coli, Salmonella enteritidis, Pseudomonas aeruginosa and Klebsiella oxytoca) were subjected to antibiotic susceptibility test. Resistant strains were further evaluated against different plant extracts in comparison to Meropenem (control) using agar diffusion method. RESULTS: E. coli had the highest occurrence (53 %), followed by P. aeruginosa (25 %) and then S. enteritidis (13 %) while the least was K. oxytoca (9 %). Virtually all the isolates exhibited multi-antibiotic resistance (MAR) with gross resistance to Amoxicillin, Erythromycin and Cefuroxine. P. aeruginosa (75 %), S. enteritidis (75 %) and E. coli (63 %), had the highest MAR. Out of the 11 (100 %) plant extracts evaluated, 7 (64 %) were outstanding and showed varied levels of antibacterial activity. Specifically, methanol extract of Mangifera indica Julie cultivar leaf (MJLM) had the highest antibacterial activity, followed by Euadenia trifoliata stem bark (TB03) and Euadenia eminens leaf (TB05). P. aeruginosa was highly susceptible (81.81 %) to the extracts, followed by S. enteritidis (63.64 %) and then E. coli (27.27 %). CONCLUSIONS: MJLM and other extracts have proven to be promising extracts in which to search for bioactive components that can be developed into therapeutic drugs. This may help in the management of antibiotic resistant bacterial isolates from poultry chicken threatening public health.