A) In Bacillus species, Spo0A is activated via the phosphorelay, with kinases KinA, KinB, KinC, KinD, and KinE transferring phosphate to Spo0A via Spo0F and Spo0B, while the Rap and Spo0E phosphatases repress Spo0A activation. B) In C. difficile, the phosphotransfer proteins PtpA and PtpB act in coordination to prevent Spo0A activation, with PtpC and Spo0E also acting to repress Spo0A activity. RstA promotes sporulation through an unknown mechanism, and a yet unidentified activating factor is hypothesized to phosphorylate Spo0A.