Impacts of <i>perR</i> on oxygen sensitivity, gene expression, and murine infection in <i>Clostridioides difficile</i> 630∆ <i>erm</i>

<i>Clostridioides difficile</i> infection (CDI), characterized by colitis and diarrhea, afflicts approximately half a million people in the USA every year, burdening both individuals and the healthcare system. <i>C. difficile</i> 630Δ<i>erm</i> is an erythromycin-sensitive variant of the clinical isolate <i>C. difficile</i> 630 and is commonly used in the <i>C. difficile</i> research community due to its genetic tractability. 630Δ<i>erm</i> possesses a point mutation in <i>perR</i>, an autoregulated transcriptional repressor that regulates oxidative stress resistance genes. This point mutation results in a constitutively de-repressed PerR operon in 630Δ<i>erm</i>. To address the impacts of <i>perR</i> on phenotypes relevant for oxygen tolerance and relevant to a murine model of CDI, we corrected the point mutant to restore PerR function in 630∆<i>erm</i> (herein, 630∆<i>erm perR</i>^WT). We demonstrate that there is no difference in growth between 630Δ<i>erm</i> and 630Δ<i>erm perR</i>^WT under anaerobic conditions or when exposed to concentrations of O₂ that mimic those found near the surface of the colonic epithelium. However, 630∆<i>erm perR</i>^WT is more sensitive to ambient oxygen than 630∆<i>erm</i>, which coincides with alterations in expression of a variety of <i>perR</i>-dependent and <i>perR</i>-independent genes. Finally, we show that 630∆<i>erm</i> and 630∆<i>erm perR</i>^WT do not differ in their ability to infect and cause disease in a well-established murine model of CDI. Together, these data support the hypothesis that the <i>perR</i> mutation in 630∆<i>erm</i> arose as a result of exposure to ambient oxygen and that the <i>perR</i> mutation in 630∆<i>erm</i> is unlikely to impact CDI-relevant phenotypes in laboratory studies.IMPORTANCE<i>Clostridioides difficile</i> is a diarrheal pathogen and a major public health concern. To improve humans' understanding of <i>C. difficile</i>, a variety of <i>C. difficile</i> isolates are used in research, including <i>C. difficile</i> 630Δ<i>erm</i>. 630Δ<i>erm</i> is a derivative of the clinical isolate 630 and is commonly studied because it is genetically manipulable. Previous work showed that a mutation in <i>perR</i> in 630Δ<i>erm</i> results in a dysregulated oxidative stress response, but no work has been done to characterize <i>perR</i>-dependent effects on the transcriptome or to determine impacts of <i>perR</i> during infection. Here, we identify transcriptomic differences between 630∆<i>erm and</i> 630∆<i>erm perR</i>^WT exposed to ambient oxygen and demonstrate that there is no strain-based difference in burdens in murine <i>C. difficile</i> infection.