Isolation and characterization of Bacillus subtilis RZS-01 isolate from agricultural soil in Bangladesh with potent antimicrobial activities

Plant diseases caused by pathogenic microorganisms, including bacteria, fungi, and other invaders, pose a severe threat to agricultural productivity by impeding plant growth and reducing crop yield. To combat these detrimental effects, harnessing the bioactive properties of indigenous microbial species can play a crucial role in defending plants against pathogenic attacks. In this study, we isolated three Bacillus subtilis strains from the rhizospheric soil of agricultural fields in BARI, Bangladesh. Initial in vitro assessments on culture plates revealed a promising Gram-positive B. subtilis isolate, designated as RZS-01, which displayed potent antibacterial and antifungal effects. Through an integrated approach encompassing biochemical, morphological, and molecular analyses, including 16 s rRNA sequencing and phylogenetic relationships, we confirmed RZS-01 as a member of the Bacillus genus. Notably, this isolate exhibited significant antimicrobial activity against 80% of tested microorganisms, including several notorious plant pathogens such as R. solani, B. cinerea, S. sclerotiorum, Pseudomonas spp., and Xanthomonas spp., as demonstrated in vitro. In the antibiotic susceptibility assay, RZS-01 showed varied sensitivity, with potent antibacterial activity against levofloxacin, nalidixic acid, erythromycin, and ciprofloxacin, resistance to norfloxacin and amoxicillin, and intermediate sensitivity to other antibiotics. These findings pave the way for the development of robust therapeutics aimed at preventing microbial infections in plants, thus enhancing agricultural sustainability and productivity.