# Impacts of perR on oxygen sensitivity, gene expression, and murine infection in Clostridioides difficile 630∆erm

## TL;DR

Researchers studied how a mutation in the perR gene affects Clostridioides difficile's oxygen sensitivity and infection in mice.

## Contribution

The study identifies transcriptomic differences due to a perR mutation and shows no impact on infection in a murine model.

## Key findings

- Restoring PerR function in 630Δerm does not affect growth under anaerobic or low-oxygen conditions.
- 630Δerm perRWT is more sensitive to ambient oxygen and shows altered gene expression.
- The perR mutation does not impact infection or disease in a murine model of CDI.

## Abstract

Clostridioides difficile 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. C. difficile 630Δerm is an erythromycin-sensitive variant of the clinical isolate C. difficile 630 and is commonly used in the C. difficile research community due to its genetic tractability. 630Δerm possesses a point mutation in perR, an autoregulated transcriptional repressor that regulates oxidative stress resistance genes. This point mutation results in a constitutively de-repressed PerR operon in 630Δerm. To address the impacts of perR 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∆erm (herein, 630∆erm perRWT). We demonstrate that there is no difference in growth between 630Δerm and 630Δerm perRWT under anaerobic conditions or when exposed to concentrations of O2 that mimic those found near the surface of the colonic epithelium. However, 630∆erm perRWT is more sensitive to ambient oxygen than 630∆erm, which coincides with alterations in expression of a variety of perR-dependent and perR-independent genes. Finally, we show that 630∆erm and 630∆erm perRWT 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 perR mutation in 630∆erm arose as a result of exposure to ambient oxygen and that the perR mutation in 630∆erm is unlikely to impact CDI-relevant phenotypes in laboratory studies.

Clostridioides difficile is a diarrheal pathogen and a major public health concern. To improve humans’ understanding of C. difficile, a variety of C. difficile isolates are used in research, including C. difficile 630Δerm. 630Δerm is a derivative of the clinical isolate 630 and is commonly studied because it is genetically manipulable. Previous work showed that a mutation in perR in 630Δerm results in a dysregulated oxidative stress response, but no work has been done to characterize perR-dependent effects on the transcriptome or to determine impacts of perR during infection. Here, we identify transcriptomic differences between 630∆erm and 630∆erm perRWT exposed to ambient oxygen and demonstrate that there is no strain-based difference in burdens in murine C. difficile infection.