MutL significantly regulates the formation of biofilms in B. subtilis YT1

As a crucial and integral adaptation for thriving in diverse habitats, whether for survival or disease prevention and control, biofilm plays a vital role for most biocontrol bacteria, such as B. subtilis , Bacillus amyloliquefaciens , and plant-growth-promoting rhizobacteria (PGPR). However, the process of biofilm formation is intricate, and its regulatory mechanism remains unclear. In this study, we discovered that the regulatory protein MutL significantly influenced biofilm formation and exhibited a diminished colonization effectiveness on rice leaves. The mutant, lacking protein MutL expression, was unable to form biofilm with normal morphology and yielded only a quarter of the biofilm weight observed in the wild type B.subtilis YT1. In a petri dish confrontation assay examining the inhibitory effects on Rhizoctonia solani , no significant differences were observed between the mutant strain and the wild type YT1. Furthermore, through GFP fluorescent labeling technology, we conducted additional colonization tests, which demonstrated that the mutant failed to colonize rice stems effectively in the presence of R. solani . We hypothesize that the negative impact on biofilm formation resulted in inadequate colonization of rice stems, this combination accounts for the poor biocontrol efficacy against rice sheath blight, but it does not affect the normal growth of the strain or other biological phenotypes.