RstA Regulation ofClostridioides difficileToxin Production and Sporulation in Phenotypically Diverse Strains

ABSTRACT The anaerobic spore-former, Clostridioides difficile , causes significant diarrheal disease in humans and other mammals. Infection begins with the ingestion of dormant spores which subsequently germinate within the host gastrointestinal tract. Here, the vegetative cells proliferate and secrete two exotoxins, TcdA and TcdB, which cause disease symptoms. Although spore formation and toxin production are critical for C. difficile pathogenesis, the regulatory links between these two physiological processes are not well understood and are strain-dependent. Previously, we identified a conserved C. difficile regulator, RstA, that promotes sporulation initiation through an unknown mechanism and directly and indirectly represses toxin gene transcription in the historical isolate, 630Δ erm . To test whether perceived strain-dependent differences in toxin production and sporulation are mediated by RstA, we created an rstA mutant in the epidemic 027 ribotype strain, R20291. RstA affects sporulation and toxin gene expression similarly in R20291, although more robust regulatory effects are observed in this strain than in 630Δ erm . Reporter assays measuring transcriptional regulation of tcdR , the sigma factor essential for toxin gene expression, identified sequence-dependent effects influencing repression by RstA and CodY, a global nutritional sensor, in four diverse C. difficile strains. We provide evidence that RstA contributes to tcdR bistability in R20291 by biasing cells to a toxin-OFF state. Finally, sequence-dependent and strain-dependent differences were evident in RstA negative autoregulation of rstA transcription. Our data establish RstA as an important regulator of C. difficile virulence traits, and implicate RstA as a contributor to the variety of sporulation and toxin phenotypes observed in distinct isolates. IMPORTANCE Two critical traits of Clostridioides difficile pathogenesis are the production of toxins, which cause disease symptoms, and the formation of spores, which permit survival outside of the gastrointestinal tract. The multifunctional regulator, RstA, promotes sporulation and prevents toxin production in the historical strain, 630Δ erm . Here, we show that RstA functions similarly in an epidemic isolate, R20291, although strain-specific effects on toxin and rstA expression are evident. Our data demonstrate that sequence-specific differences within the promoter for the toxin regulator, TcdR, contribute to regulation of toxin production by RstA and CodY. These sequence differences account for some of the variability in toxin production among isolates, and may allow strains to differentially control toxin production in response to a variety of signals.