Genomic and phenotypic analysis of Bacillus strains from Protaetia brevitarsis frass reveals plant growth promoting potential and biocontrol activity against Fusarium wheat crown rot

BACKGROUND: The search for novel microbial agents is essential for advancing sustainable agriculture. Insect frass, a nutrient-rich byproduct, represents a promising yet underexplored reservoir of beneficial microbes. This study explores the potential of frass derived from Protaetia brevitarsis larvae (PBL) as a source of multifunctional Bacillus strains that exhibit antagonistic activity against fungal pathogens and plant growth promotion. RESULTS: A total of 47 bacterial strains, including 37 Bacillus strains, were isolated from PBL frass. Among these, nine strains belonging to five distinct Bacillus species, namely B. velezensis, B. subtilis, B. paralicheniformis, B. safensis and members of the B. pumilus group, exhibited significant in vitro antagonism against Fusarium graminearum. These nine Bacillus strains displayed diverse plant growth-promoting traits, such as indole-3-acetic acid and siderophore production, as well as phosphate solubilization. In planta assays confirmed their ability to promote wheat growth and suppress Fusarium crown rot, with strains PBF3, PBF5 and PBF9 achieving biocontrol efficacies of 70.32%, 69.03% and 66.45%, respectively. Complete genome sequencing of the elite strain PBF3 revealed a genome size of 3.845 Mb, harboring 4841 protein-coding genes. Average nucleotide identity analysis confirmed that PBF3 represents a novel strain within the species B. safensis. Genomic analysis identified three secondary metabolite biosynthesis gene clusters associated with known antimicrobial properties, along with a repertoire of putative novel compounds, suggesting potentially unique bioactivities. Genome mining further uncovered multiple key genes involved in plant growth promotion, root colonization, biofilm formation and stress tolerance. CONCLUSION: PBL frass represents a valuable Bacillus strain source for the green control of Fusarium wheat crown rot. The convergence of phenotypic advantages and genomic potential in these strains underscores their promise for the development of dual-purpose bioinoculants that combine plant growth promotion with the biocontrol of plant diseases, providing a sustainable solution for crop protection. © 2026 Society of Chemical Industry.