The biocontrol agent Bacillus velezensis T-5 changes the soil bacterial community composition by affecting the tomato root exudate profile

Aims: Root exudates modulate the interaction between plants, pathogens, and beneficial microbes. In this study, we tested whether tomato plants modify their root exudates in the presence of Bacillus velezensis T-5, a biocontrol agent of bacterial wilt disease, and whether the changes in root exudates alter the soil bacterial community composition. Methods: We profiled exudates from non-inoculated and B. velezensis T-5-inoculated tomato plants using high-performance liquid chromatography analyses. We then added root exudates to unplanted soil and examined the soil bacterial community composition using 16S rRNA gene amplicon sequencing. The effects of exudate compounds generated after inoculation with strain T-5 on the pathogen of bacterial wilt were tested in vitro. Results: The presence of strain T-5 changed the profile of tomato root exudates and increased the secretion of cinnamic acid. Compared to non-inoculated root exudates, T-5-inoculated root exudates increased the soil bacterial diversity, changed the soil bacterial community composition, and increased the relative abundance of potentially beneficial bacteria. Importantly, cinnamic acid inhibited pathogen growth while promoting the growth of strain T-5 in a dose-dependent manner. Conclusion: Changes in root exudate composition induced by biocontrol agents may suppress pathogens by direct inhibition and by indirectly altering the rhizosphere microbiome composition.