Construction of engineered <i>Bacillus velezensis</i> XY40-1 and the role of <i>degQ</i> in enhancing fengycin synthesis and pepper disease resistance

AIMS: This study investigated the interaction between the biocontrol bacterium Bacillus velezensis XY40-1 and pepper plants, with a focus on enhancing biocontrol efficacy and plant growth-promoting traits through genetic engineering. Specifically, the role of the endogenous gene degQ, a regulator of fengycin biosynthesis, was examined to determine its contribution to antifungal activity and plant colonization. METHODS AND RESULTS: A genetic engineering system was developed for XY40-1, with an optimized transformation method enabling efficient introduction of both exogenous and endogenous genes. Stable GFP expression facilitated colonization studies, showing that XY40-1 spreads from roots to shoots via the vascular system and achieves full colonization within 7 days. Functional analysis of degQ involved construction of deletion (ΔdegQ) and overexpression (p43:: degQ) mutants. The ΔdegQ strain exhibited reduced biofilm formation, altered morphology, and weakened pathogen inhibition, while the p43:: degQ strain retained wild-type morphology but showed superior pathogen suppression, surpassing chemical pesticides. RT-qPCR and ultra-performance liquid chromatography-MS/MS confirmed that fengycin production in p43:: degQ was 3-4 times higher than in the wild type, whereas ΔdegQ produced negligible levels. CONCLUSIONS: The findings demonstrate that degQ plays a central role in regulating fengycin synthesis, biofilm formation, and biocontrol activity in XY40-1.