SpoIVA-SipL Complex Formation Is Essential for Clostridioides difficile Spore Assembly

Abstract

The metabolically dormant spore form of the major nosocomial pathogen Clostridioides difficile is its major infectious particle. However, the mechanisms controlling the formation of this resistant cell type are not well understood, particularly with respect to its outermost layer, the spore coat. We previously identified two spore-morphogenetic proteins in C. difficile : SpoIVA, which is conserved in all spore-forming organisms, and SipL, which is conserved only in the clostridia. Both SpoIVA and SipL are essential for heat-resistant spore formation and directly interact through SipL’s C-terminal LysM domain. In this study, we demonstrate that the LysM domain is critical for SipL and SpoIVA function, likely by helping recruit SipL to the forespore during spore morphogenesis. We further identified residues within the LysM domain that are important for binding SpoIVA and, thus, functional spore formation. These findings provide important insight into the molecular mechanisms controlling the assembly of infectious C. difficile spores.