CotL, a new morphogenetic coat protein of Clostridium difficile

The strict anaerobe Clostridium difficile is an important nosocomial enteropathogen that has become the most common cause of antibiotic-associated diarrhea. The oxygen-resistant C. difficile spores play a central role in the infectious cycle, contributing to transmission, infection and recurrence. The spore surface layers, coat and exosporium, enable resistance of the spores to extreme physical and chemical stresses. Despite the critical importance of the spore in C. difficile infection, little is known about the mechanisms that orchestrate the assembly of its external layers. In this study, we identified and characterized a new C. difficile spore protein, named CotL, which is required for the assembly of the spore surface layers. The cotL gene was expressed in the mother cell compartment under the dual control of σE and σK. The CotL protein was localized in the C. difficile spore coat and cotL mutant spores had a major morphologic defect at the level of the coat/exosporium layers, as observed by transmission electron microscopy. Accordingly, spores of the cotL mutant contained a reduced amount of several proteins of the coat and exosporium, including CotB, CotE and CdeC. Additionally, cotL inactivation resulted in a defect in localization of late spore coat proteins in sporulating cells. Finally, spores of the cotL mutant were more sensitive to lysozyme and were impaired in germination. These defects are most likely associated with the structurally altered coat. Collectively, these results strongly suggest that CotL is a morphogenetic protein essential for the assembly of the spore coat in C. difficile.