Isolation and Genome-Based Characterization of Bacillus velezensis AN6 for Its Biocontrol Potential Against Multiple...

Biological control is an effective and environmentally friendly strategy for managing plant diseases. In this study, a broad-spectrum antagonistic bacterium, designated strain AN6, was isolated from rice plants and exhibited potent inhibitory activity against a variety of phytopathogens. In Oxford cup assays, AN6 suppressed the growth of Xanthomonas oryzae pv. oryzae (Xoo) by 73.60%, and its cell-free culture filtrate caused pronounced morphological deformation in the bacterial cells. Further in vitro assays, including dual-culture assays, volatile organic compound (VOC) assays, and cell-free supernatant (CFS) assays, demonstrated that AN6 also exerted strong antifungal effects against several pathogenic fungi. In addition, the strain was found to produce proteases and siderophores, which may contribute to its antagonistic capabilities. Taxonomic identification based on morphological traits, 16S rRNA and gyrA gene sequencing, average nucleotide identity (ANI), in silico DNA-DNA hybridization (isDDH), and phylogenetic analysis classified strain AN6 as Bacillus velezensis. Whole-genome sequencing revealed that AN6 harbors a 3,929,788 bp genome comprising 4025 protein-coding genes with a GC content of 46.50%. Thirteen biosynthetic gene clusters (BGCs) associated with the production of secondary metabolites-such as nonribosomal peptides, polyketides, and dipeptide antibiotics-were identified. The pot experiment further validated the biocontrol potential of AN6, achieving an 80.49% reduction in rice bacterial blight caused by Xanthomonas oryzae pv. oryzae. Collectively, these results indicate that B. velezensis AN6 is a promising candidate for development as a highly effective biocontrol agent for the integrated management of diverse plant diseases.