# Phase variation of virulence factors in Clostridium difficile

> **NIH NIH R01** · UNIV OF NORTH CAROLINA CHAPEL HILL · 2022 · $415,492

## Abstract

PROJECT SUMMARY
Clostridium difficile is a major public health threat, causing disease ranging from mild diarrhea to
pseudomembranous colitis. C. difficile disease symptoms are largely mediated by the secreted cytotoxins,
TcdA and TcdB. Many aspects of the pathogenicity of this bacterium remains poorly understood, including how
C. difficile regulates the production of the toxins and other virulence factors. Toxin gene expression is linked to
expression of flagellar genes via the flagellar sigma factor sigma-D, which is encoded in the flgB operon. Thus,
factors that regulate the expression of the flgB operon will impact toxin production in addition to flagellar
motility. Our long-term goal is to determine how C. difficile coordinately regulates flagellum and toxin gene
expression, as these mechanisms are likely fundamental to pathogenesis. We recently showed that flagellar
gene expression is subject to phase variation through site-specific DNA recombination of an invertible
sequence upstream of the flgB operon. Notably, inversion of the DNA sequence, which we term the “flagellar
switch”, also impacts the production of toxins essential for virulence. We identified RecV as the DNA
recombinase that mediates inversion of the flagellar switch, and we have begun to define the mechanism by
which the orientation of the flagellar switch sequence controls gene expression. Our central hypothesis is that
phase variation of flagellum and toxin production is critical to C. difficile pathogenesis, and consequently
interfering with the ability of C. difficile to phase vary will attenuate one or more aspects of virulence. While
flagella and/or motility may be important for some aspects of infection, downregulation of flagella is likely vital
for C. difficile to evade host immune recognition. Toxin production may similarly be beneficial or detrimental to
C. difficile during different stages of infection. The objective of this proposal is to define the molecular
mechanisms underlying phase variation and to evaluate the impact of phase variation on host colonization and
virulence. This proposal is innovative because it represents an entirely new area of investigation toward
understanding C. difficile disease: phase variable expression of flagella and toxins. Completion of the proposed
studies will provide much needed mechanistic information on how C. difficile controls virulence factor
production during infection, and may expose potential targets for inhibition of intestinal colonization and toxin
production to facilitate efforts to combat this increasingly problematic pathogen.

## Key facts

- **NIH application ID:** 10463619
- **Project number:** 5R01AI107029-10
- **Recipient organization:** UNIV OF NORTH CAROLINA CHAPEL HILL
- **Principal Investigator:** RITA TAMAYO
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $415,492
- **Award type:** 5
- **Project period:** 2013-05-20 → 2024-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10463619

## Citation

> US National Institutes of Health, RePORTER application 10463619, Phase variation of virulence factors in Clostridium difficile (5R01AI107029-10). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10463619. Licensed CC0.

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