Intestinal bacterium Bacillus siamensis M54 from Allomyrina dichotoma is a potential biocontrol agent against maize stalk rot

Maize stalk rot, caused by Fusarium spp., is a significant disease that adversely impacts the yield and quality of corn. Biological control plays a crucial role in managing numerous crop diseases, including maize stalk rot. Biocontrol agents are predominantly derived from soil and plant tissues, with limited reports on isolating highly efficient biocontrol agents from insects. In this study, 144 bacterial strains were isolated from the intestinal tract of third instar larvae of Allomyrina dichotoma. Through dual culture tests, twelve strains exhibiting strong antagonism against two maize stalk rot pathogens, F. graminearum and F. verticillioides, were identified. Among them, the M54 strain exhibited the most potent antagonistic effect against the two pathogenic fungi and was identified as Bacillus siamensis through 16S rRNA gene sequence analysis. The complete genome for M54 was assembled using PacBio single-molecule real-time (SMRT) and Illumina sequencing technologies. Whole genome phylogenetic analysis further confirmed M54 was B. siamensis. Microscopic examination revealed that M54 had the ability to inhibit the fungal spore germination and hyphal formation. Furthermore, M54 exhibited effective colonization in the maize rhizosphere and enhanced maize growth. It showed that treatment with M54 significantly suppressed lesion expansion induced by F. graminearum on maize stalks in the seedling and adult plant assays. Genomic analysis using antiSMASH revealed 11 gene clusters for secondary metabolite synthesis. This study provides a novel approach for isolating biocontrol agents to manage plant diseases and highlights B. siamensis M54 as a potential efficient biocontrol agent for maize stalk rot.