Genomic, LC-MS, and FTIR Analysis of Plant Probiotic Potential of Bacillus albus for Managing Xanthomonas oryzae via Different Modes of Application in Rice (Oryza sativa L.).

Xanthomonas oryzae causes tremendous damage in rice plants (Oryza sativa L). Therefore, this study is focused on siderophore-producing Bacillus albus (CWTS 10) for managing BLB disease caused by X. oryzae. Both B. albus and its crude siderophore (methanolic and diethyl ether) extracts inhibited X. oryzae (10-12 mm). Fourier transform infrared spectroscopy (FTIR) analysis of the extracts indicated the presence of catecholate siderophore functional groups. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed the presence of antimicrobial compounds such as 2-deoxystreptamine, miserotoxin, fumitremorgin C, pipercide, pipernonaline, gingerone A, and deoxyvasicinone. Complete genome sequencing revealed the gene clusters for antibiotic, siderophore, antibacterial, antifungal, and secondary metabolite production. An in vivo study revealed that bacteria (CWTS 10) and their siderophore extracts effectively inhibited X. oryzae. The mode of application of bacterial or siderophore extracts in terms of DI and DSI percentage was as follows: soak method > inoculation method > spray method. In addition to providing enhanced antagonistic activity, there was a significant increase in root and shoot length and weight (wet and dry) of treated plants compared to control plants challenged with X. oryzae. Thus, the results clearly indicate that siderophore-producing B. albus and its siderophore extracts strongly inhibited X. oryzae. However, further field experiments are required before being formulated to protect rice crops from X. oryzae.

Complete genome sequencing of Bacillus subtilis (CWTS 5), a siderophore-producing bacterium triggers antagonistic potential against Ralstonia solanacearum.

AIM: The aims of this study were to explore the antagonistic potential of siderophore-producing Bacillus subtilis (CWTS 5) for the suppression of Ralstonia solanacearum and to explore the mechanisms of inhibition by FTIR, LC-MS, and whole genome analysis. METHODS AND RESULTS: A siderophore-producing B. subtilis (CWTS 5) possessing several plant growth-promoting properties such as IAA and ACC deaminase production, phosphate solubilization, and nitrogen fixation was assessed for its inhibitory effect against R. solanacearum, and its mechanisms were explored by in vitro and in vivo analyses. The active secondary metabolites in the siderophore extracts were identified as 2-deoxystreptamine, miserotoxin, fumitremorgin C, pipercide, pipernonaline, gingerone A, and deoxyvasicinone by LC-MS analysis. The Arnow's test and antiSMASH analysis confirmed the presence of catecholate siderophores, and the functional groups determined by FTIR spectroscopy confirmed the presence of secondary metabolites in the siderophore extract possessing antagonistic effect. The complete genome sequence of CWTS 5 revealed the gene clusters responsible for siderophore, antibiotics, secondary metabolite production, and antibacterial and antifungal metabolites. Furthermore, the evaluation of CWTS 5 against R. solanacearum in pot studies demonstrated 40.0% reduced disease severity index (DSI) by CWTS 5, methanolic extract (DSI-26.6%), ethyl acetate extract (DSI-20.0%), and increased plant growth such as root and shoot length, wet weight and dry weight of Solanum lycopersicum L. owing to its antagonistic potential. This genomic insight will support future studies on the application of B. subtilis as a plant growth promoter and biocontrol agent against R. solanacearum for bacterial wilt management. CONCLUSION: The results of this study revealed that B. subtilis (CWTS 5) possesses multiple mechanisms that control R. solanacearum, reduce disease incidence, and improve S. lycopersicum growth.

Bacteria isolated from e-waste soil enhance plant growth and mobilize trace metals in e-waste-amended soils.

Worldwide accumulation of e-waste poses a major threat to environmental health. However, printed circuit boards contain precious metals, such as gold, and silver, and also contain micronutrient metal elements, such as Fe, Cu, Zn, etc. Therefore, the present study investigated the effects of e-waste-tolerant bacteria (ETB) on promoting plant growth in e-waste-amended soils and mobilizing trace metals into the plants. For this, a total of 18 bacteria were isolated and screened for e-waste tolerance. Screening for plant growth-promoting properties revealed the production of indole-3-acetic acid-like compounds, siderophore production, and phosphate solubilization. Identification based on 16S rRNA gene sequencing revealed that all isolates belonged to the genus Bacillus. Pot experiment revealed that the treated seeds showed the enhancement of chili plants root growth ranging from 106.55 to 208.07% compared to control plants (e-waste) and 0.0 to 47.90% (without e-waste). A similar enhancement was also observed in the shoot length, and size of the leaf compared to e-waste amended control plants. Inoculation of ETB significantly (p < 0.05) mobilized Fe, Zn, Cu, and Ni into chili plants. The identified ETB could be used to mitigate the toxicity posed by the e-waste, enhancing plant growth and mobilization of micronutrients into plants from e-waste.

Bacillus species identified in this study are the potential e-tolerant (PCB) PGP bacteria. Inoculation of e-tolerant bacteria resulted in increased plant growth attributes and biomass index in e-waste amended soil. Bacterial inoculation also showed maximum uptake of Cu, Fe, Zn, and Ni from the e-waste amended soil. This study demonstrated that micronutrients can be fortified/mobilized from e-waste using PGP bacteria.