[Seminar] The alternative sigma factor σB plays a crucial role in adaptive strategies of Clostridium difficile during gut infection

Title: The alternative sigma factor σB plays a crucial role in adaptive strategies of Clostridium difficile during gut infection
 

Speaker: Isabelle Martin-Verstraete

Affiliation: Institut Pasteur, Paris, France

Abstract:

Clostridium difficile is a major cause of diarrhoea associated with antibiotherapy. After germination of C. difficile spores in the gut, vegetative cells are exposed to several stresses including pH variations, hyperosmolarity, bile salts, as well as antimicrobial peptides, ROS and RNS produced by the host during inflammation. C. difficile can survive by inducing protection, detoxification, and repair systems. In several firmicutes, these systems are controlled by the general stress response involving σ^B. We recently studied the role of σ^B in the physiopathology of C. difficile¹. We showed that the survival of the sig^B mutant during the stationary phase was reduced. Using a transcriptome analysis, we showed that σ^B controls the expression of ~25% of genes including genes involved in sporulation, metabolism, cell surface biogenesis, and the management of stresses. By contrast, σ^B does not control toxin gene expression. In agreement with the up-regulation of sporulation genes, the sporulation efficiency is higher in the sigB mutant than in the wild-type strain. sig^B inactivation also led to increased sensitivity to acidification, cationic antimicrobial peptides, NO and ROS. In addition, we showed for the first time that σ^B also plays a crucial role in O2 tolerance in this strict anaerobe. We also demonstrated that the fitness of colonisation by the sig^B mutant is greatly affected in a dixenic mouse model of colonisation when compared to the wild-type strain1. Our results highlight that σ^B serves as a key regulator of gut colonisation by coordinating several processes likely required for adaptation and survival of bacteria within the gut. In addition, we established that proteins involved in stress response encoded by σ^B-transcribed genes are present in the spore coat. Interestingly, these genes as well as the sig^B gene are specifically expressed in the mother cell during sporulation in agreement with the localization of the corresponding protein synthesized under σ^B control at the surface of the spore.

Finally, we showed the conservation of the partner switching mechanism involving an anti-σ factor RsbW capturing σ^B and the phosphorylated/dephosphorylated state of an anti-anti-σ RsbV controlled by a phosphatase. We started to decipher the signalling pathways responsible in the release and activation of σB in response to stressful stimuli in C. difficile.

Kint N. et al., The alternative sigma factor σ^B plays a crucial role in adaptive strategies of Clostridium difficile during gut infection. Environ Microbiol, 2017.