Genomic and Antifungal Characterization of Bacillus velezensis CCLB-1 Isolated from the Gut of Cicindela chinensis

Abstract

Insect-associated microbiota represents a promising yet relatively unexplored reservoir of bioactive agents for sustainable agriculture. In this study, we performed a comprehensive genomic and phenotypic characterization of Bacillus velezensis CCLB-1, a novel bacterial strain isolated from the gut of the tiger beetle (Cicindela chinensis DeGeer), focusing on its multi-functional antifungal traits. Taxonomic identification using 16S ribosomal RNA sequencing, Average Nucleotide Identity, and digital DNA-DNA hybridization confirmed its distinct position within the B. velezensis group. Hybrid whole-genome sequencing revealed a 3.98 Mb circular chromosome encoding critical biosynthetic gene clusters for antifungal metabolites, alongside remarkable environmental adaptability, including superior salt tolerance (up to 7% NaCl). In vitro confrontation assays demonstrated that strain CCLB-1 exhibits potent broad-spectrum antifungal activity, significantly inhibiting the mycelial growth of Alternaria alternata (59.42%) and Colletotrichum truncatum (57.00%). Furthermore, in vivo assays on pepper (Capsicum annuum L.) fruits validated its robust protective efficacy against anthracnose by markedly reducing disease severity and inducing fungal hyphal lysis. Taken together, these findings elucidate the genomic basis and functional potential of a predatory insect-derived B. velezensis strain, providing critical insights into the utilization of non-rhizosphere microbial resources for eco-friendly plant disease management.