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Open Access Research article

The LexA regulated genes of the Clostridium difficile

Beata M Walter1, Maja Rupnik123, Vesna Hodnik4, Gregor Anderluh45, Bruno Dupuy6, Nejc Paulič4, Darja Žgur-Bertok4 and Matej Butala4*

Author Affiliations

1 Institute of Public Health Maribor, Centre for Microbiology, Maribor, Slovenia

2 Faculty of Medicine, University of Maribor, Maribor, Slovenia

3 Centre of Excellence for Integrated Approaches in Chemistry and Biology of Proteins, Ljubljana, Slovenia

4 Biotechnical Faculty, University of Ljubljana, Department of Biology, Ljubljana, Slovenia

5 National Institute of Chemistry, Ljubljana, Slovenia

6 Laboratoire Pathogenèse des Bactéries Anaérobies, Département de Microbiologie, Institut Pasteur, Paris, France

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BMC Microbiology 2014, 14:88  doi:10.1186/1471-2180-14-88

Published: 8 April 2014

Abstract

Background

The SOS response including two main proteins LexA and RecA, maintains the integrity of bacterial genomes after DNA damage due to metabolic or environmental assaults. Additionally, derepression of LexA-regulated genes can result in mutations, genetic exchange and expression of virulence factors. Here we describe the first comprehensive description of the in silico LexA regulon in Clostridium difficile, an important human pathogen.

Results

We grouped thirty C. difficile strains from different ribotypes and toxinotypes into three clusters according to lexA gene/protein variability. We applied in silico analysis coupled to surface plasmon resonance spectroscopy (SPR) and determined 16 LexA binding sites in C. difficile. Our data indicate that strains within the cluster, as defined by LexA variability, harbour several specific LexA regulon genes. In addition to core SOS genes: lexA, recA, ruvCA and uvrBA, we identified a LexA binding site on the pathogenicity locus (PaLoc) and in the putative promoter region of several genes involved in housekeeping, sporulation and antibiotic resistance.

Conclusions

Results presented here suggest that in C. difficile LexA is not merely a regulator of the DNA damage response genes but also controls the expression of dozen genes involved in various other biological functions. Our in vitro results indicate that in C. difficile inactivation of LexA repressor depends on repressor`s dissociation from the operators. We report that the repressor`s dissociation rates from operators differentiate, thus the determined LexA-DNA dissociation constants imply on the timing of SOS gene expression in C. difficile.

Keywords:
Clostridium difficile; Antibiotic resistance; Toxin regulation; SOS system; Surface plasmon resonance; LexA repressor