SpoIIID-mediated regulation of σK function duringClostridium difficilesporulation

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Abstract

Summary

The spore-forming bacterial pathogenClostridium difficileis a leading cause of health-care-associated diarrhea worldwide. AlthoughC. difficilespore formation is essential for disease transmission, the regulatory pathways that control this developmental process have only been partially characterized. In the well-studied spore-formerBacillus subtilis, the highly conserved σE, SpoIIID and σK regulatory proteins control gene expression in the mother cell to ensure proper spore formation. To define the precise requirement for SpoIIID and σK duringC. difficilesporulation, we analyzedspoIIIDandsigKmutants using heterologous expression systems and RNA-Seq transcriptional profiling. These analyses revealed that expression ofsigKfrom a SpoIIID-independent promoter largely bypasses the need for SpoIIID to produce heat-resistant spores. We also observed that σK is active upon translation, suggesting that SpoIIID primarily functions to activatesigK. SpoIIID nevertheless plays auxiliary roles during sporulation, as it enhances levels of the exosporium morphogenetic protein CdeC in a σK-dependent manner. Analyses of purified spores further revealed that SpoIIID and σK control the adherence of the CotB coat protein toC. difficilespores, indicating that these proteins regulate multiple stages of spore formation. Collectively, these results highlight that diverse mechanisms control spore formation in the Firmicutes.

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