Cations and surfactin serving as signal molecules trigger quorum sensing in Bacillus amyloliquefaciens

Microorganisms including Bacillus can produce signal molecules such as surfactin, resulting in the variation of membrane potential to trigger quorum sensing such as biofilm formation and sporulation in response to the environment stresses. However, biosynthesis of surfactin requires multiple resources such as huge enzyme complex, amino acids, fatty acids, and energy. Insufficient resources in the natural soil environment restrain biosynthesis of surfactin. When surfactin is inadequate, cations in soil might serve as substitutes to regulate quorum sensing. Our results showed that both surfactin and cations could lead to the variation of membrane potential, thus providing signals to trigger the quorum sensing such as growth, biofilm formation, and sporulation in Bacillus amyloliquefaciens. Neither KinC nor Abh was essential for surfactin or cations to trigger quorum sensing. The cation signaling pathway is only partially dependent on Spo0A, but the surfactin signaling pathway is fully dependent on this global regulator. Compared to surfactin, cations are less effective in promoting biofilm formation, but more effective to trigger sporulation in B. amyloliquefaciens. This study reveals a pathway through which cations regulate the quorum sensing in B. amyloliquefaciens in the case of insufficient surfactin in environment.