SCAN:Spore morphodynamics in relation to the infectious cycle of the human pathogen Clostridium difficile

ITQB Scan Seminar

Title: Spore morphodynamics in relation to the infectious cycle of the human pathogen Clostridium difficile

Speaker: Fátima Pereira

From: Microbial Development Laboratory

Abstract:

 Clostridium difficile is a strict anaerobic spore-forming bacterium and the major causative agent of enteric nosocomial diseases associated to antibiotic therapy in adults. Spores produced by C. difficile are highly resistant, infective and are the primary cause of transmission in health care institutions. Ingested spores are primed to germinate in the upper, aerobic parts of the intestine, upon exposure to bile salts. However, they may only complete germination in contact with a specific receptor in the mucosa of the anaerobic colon. Despite the central importance of spores in the pathogenesis of C. difficile, a detailed description of the cell differentiation process leading to spore formation in this organism is lacking. Evidence suggests that the main morphological stages of sporulation are conserved in the Clostridia. Moreover, the four cell type-specific RNA polymerase sigma factors that govern developmental gene expression in the well-studied model organism Bacillus subtilis are present in the C. difficile genome. In B. subtilis, SigF in the forespore, and SigE in the mother cell, control early stages of development, and are replaced by SigG and SigK, respectively, which control the final stages of development. Using a recently developed genetic system based on the use of type II introns, we have inactivated sigF, sigE, sigG and sigK of C. difficile. Disruption of sigF, sigE, sigG or sigK abolishes spore formation and their function largely conforms the B. subtilis paradigm. For instance, SigK may be a key regulatory protein for the assembly of the C. difficile spore surface layers. SigK appears to control the most highly expressed gene, sp17, in a mouse axenic model. Strikingly, its product, the Sp17 protein, was found to be essential for colonization of mice. We found that Sp17 is a key determinant of the assembly of the spore surface layers, and also acts as a germination suppressor. Both the altered spore surface, as well as premature germination, which may occur in the aerobic parts of the intestine, rather that in the colon, may explain the reduced colonization ability of the mutant. Sp17 therefore, establishes a direct link between the spore surface and colonization.