A family of small proteins connects c-di-GMP-signaling with sporulation in the human pathogen Clostridioides difficile

Conversely, sporulation efficiency decreased proportionally with the number of deleted small protein genes, and the strain lacking all seven genes displayed a severe sporulation defect, underscoring their cumulative and functionally redundant roles. Elevating c-di-GMP levels in the deletion mutant did not further reduce sporulation, supporting a model in which c-di-GMP inhibits spore formation by repressing the expression of this small-protein family.

Our work establishes these small proteins as critical effectors linking c-di-GMP signaling to developmental output in C. difficile. Their redundancy, conservation, and integration into riboswitch- and RgaR-mediated regulatory pathways highlight their central role in spore formation, a process essential for pathogen persistence and transmission. These findings expand the repertoire of second-messenger effectors in bacterial physiology.