Metabolite interactions mediate beneficial alliances between <i>Bacillus</i> and <i>Trichoderma</i> for effective <i>Fusarium</i> wilt control

Bacteria-Fungi Interactions play a crucial role in soil nutrient cycling and plant disease suppression. Bacillus and Trichoderma exhibit antagonism when inoculated on laboratory media, global soil sample analysis reveals a positive correlation between these two genera in addition to enhanced plant-pathogen Fusarium oxysporum suppression and plant growth promotion. Here, we assess cross-kingdom interactions within artificial model communities of Bacillus velezensis and Trichoderma guizhouense. Transcriptomic profiling revealed that in the presence of fungi, the key stress sigma factor of B. velezensis activates expression of biosynthetic genes for antimicrobial secondary metabolite production. Among these, surfactin induces T22azaphilone production in T. guizhouense that hinders oxidative stress. Both surfactin and T22azaphilone contribute to Bacillus and Trichoderma maintenance in soil in the presence of F. oxysporum. Finally, F. oxysporum-secreted fusaric acid temporarily inhibits B. velezensis growth whereas it is efficiently degraded by T. guizhouense. These metabolite-mediated interactions reveal how competing soil microorganisms could form effective alliances that ultimately enhance plant protection against soil-borne pathogens.