Strain-Dependent RstA Regulation of Clostridioides difficile Toxin Production and Sporulation.

The anaerobic spore former 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. There, the vegetative cells proliferate and secrete two exotoxins, TcdA and TcdB, which cause disease symptoms. Although spore formation and toxin production are critical for pathogenesis, the regulatory links between these two physiological processes are not well understood and are strain dependent. Previously, we identified a conserved regulator, RstA, that promotes sporulation initiation through an unknown mechanism and directly and indirectly represses toxin and motility gene transcription in the historical isolate 630Δ To test whether perceived strain-dependent differences in toxin production and sporulation are mediated by RstA, we created an mutant in the epidemic ribotype 027 strain R20291. RstA affected sporulation and toxin gene expression similarly but more robustly in R20291 than in 630Δ In contrast, no effect on motility gene expression was observed in R20291. Reporter assays measuring transcriptional regulation of , the sigma factor gene essential for toxin gene expression, identified sequence-dependent effects influencing repression by RstA and CodY, a global nutritional sensor, in four diverse strains. Finally, sequence- and strain-dependent differences were evident in RstA negative autoregulation of transcription. Altogether, our data suggest that strain-dependent differences in RstA regulation contribute to the sporulation and toxin phenotypes observed in R20291. Our data establish RstA as an important regulator of virulence traits. Two critical traits of pathogenesis are toxin production, which causes disease symptoms, and spore formation, which permits survival outside the gastrointestinal tract. The multifunctional regulator RstA promotes sporulation and prevents toxin production in the historical strain 630Δ Here, we show that RstA exhibits stronger effects on these phenotypes in an epidemic isolate, R20291, and additional strain-specific effects on toxin and expression are evident. Our data demonstrate that sequence-specific differences within the promoter for the toxin regulator TcdR contribute to the 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.