The Conserved Spore Coat Protein SpoVM Is Largely Dispensable in Spore Formation.

The spore-forming bacterial pathogen is a leading cause of health care-associated infections in the United States. In order for this obligate anaerobe to transmit infection， it must form metabolically dormant spores prior to exiting the host. A key step during this process is the assembly of a protective， multilayered proteinaceous coat around the spore. Coat assembly depends on coat morphogenetic proteins recruiting distinct subsets of coat proteins to the developing spore. While 10 coat morphogenetic proteins have been identified in ， only two of these morphogenetic proteins have homologs in the : SpoIVA and SpoVM. SpoIVA is critical for proper coat assembly and functional spore formation， but the requirement for SpoVM during this process was unknown. Here， we show that SpoVM is largely dispensable for spore formation， in contrast with . Loss of SpoVM resulted in modest decreases (~3-fold) in heat- and chloroform-resistant spore formation， while morphological defects such as coat detachment from the forespore and abnormal cortex thickness were observed in ~30% of mutant cells. Biochemical analyses revealed that SpoIVA and SpoVM directly interact， similarly to their counterparts. However， in contrast with ， SpoVM was not essential for SpoIVA to encase the forespore. Since coat morphogenesis requires SpoIVA-interacting protein L (SipL)， which is conserved exclusively in the ， but not the more broadly conserved SpoVM， our results reveal another key difference between and spore assembly pathways. The spore-forming obligate anaerobe is the leading cause of antibiotic-associated diarrheal disease in the United States. When spores are ingested by susceptible individuals， they germinate within the gut and transform into vegetative， toxin-secreting cells. During infection， must also induce spore formation to survive exit from the host. Since spore formation is essential for transmission， understanding the basic mechanisms underlying sporulation in could inform the development of therapeutic strategies targeting spores. In this study， we determine the requirement of the homolog of SpoVM， a protein that is essential for spore formation in due to its regulation of coat and cortex formation. We observed that SpoVM plays a minor role in spore formation， in contrast with ， indicating that this protein would not be a good target for inhibiting spore formation.