A Recombination Directionality Factor Controls the Cell Type-Specific Activation of σK and the Fidelity of Spore Development in Clostridium difficile.

The strict anaerobe Clostridium difficile is the most common cause of nosocomial diarrhea, and the oxygen-resistant spores that it forms have a central role in the infectious cycle. The late stages of sporulation require the mother cell regulatory protein σ^K. In Bacillus subtilis, the onset of σ^K activity requires both excision of a prophage-like element (skin^Bs) inserted in the sigK gene and proteolytical removal of an inhibitory pro-sequence. Importantly, the rearrangement is restricted to the mother cell because the skin^Bs recombinase is produced specifically in this cell. In C. difficile, σ^K lacks a pro-sequence but a skin^Cd element is present. The product of the skin^Cd gene CD1231 shares similarity with large serine recombinases. We show that CD1231 is necessary for sporulation and skin^Cd excision. However, contrary to B. subtilis, expression of CD1231 is observed in vegetative cells and in both sporangial compartments. Nevertheless, we show that skin^Cd excision is under the control of mother cell regulatory proteins σ^E and SpoIIID. We then demonstrate that σ^E and SpoIIID control the expression of the skin^Cd gene CD1234, and that this gene is required for sporulation and skin^Cd excision. CD1231 and CD1234 appear to interact and both proteins are required for skin^Cd excision while only CD1231 is necessary for skin^Cd integration. Thus, CD1234 is a recombination directionality factor that delays and restricts skin^Cd excision to the terminal mother cell. Finally, while the skin^Cd element is not essential for sporulation, deletion of skin^Cd results in premature activity of σ^K and in spores with altered surface layers. Thus, skin^Cd excision is a key element controlling the onset of σ^K activity and the fidelity of spore development. [ABSTRACT FROM AUTHOR]