SpoVG and the Kre-ComK Regulatory Module Orchestrate Production of the EPE Toxin in Bacillus subtilis

Survival of bacteria in their natural habitat requires dynamic responses and adaptation to environmental cues. In Bacillus subtilis , one adaptive strategy is cannibalism, a form of programmed cell death during post-exponential development. Cannibalism enhances multicellular differentiation by prolonging or preventing commitment to endospore formation under starvation conditions. B. subtilis produces three cannibalism toxins: the sporulation delay protein, the sporulation killing factor, and the epipeptide EPE. Production of the latter is encoded in the epeXEPAB operon. Expression of this operon is transcriptionally controlled by the stationary phase regulators Spo0A and AbrB. Here, we demonstrate that EPE production is also post-transcriptionally regulated by two RNA binding proteins, Kre and SpoVG. Deletion of comK , the master regulator of competence development, abolished EPE production. This defect was reversed by additionally deleting kre . The RNA-binding protein, Kre, binds the epeX transcript and acts as a bidirectional ComK repressor, indicating that ComK indirectly regulates EPE biosynthesis via Kre. A second RNA-binding protein, SpoVG, also binds to the epeX mRNA. While Kre acts as a negative regulator, SpoVG was essential for EPE production. These findings reveal a novel regulatory connection between competence and cannibalism, expanding our understanding of how programmed cell death is coordinated in B. subtilis .