Type IV pili proteins in Clostridioides difficile

Abstract

Clostridioides difficile is a Gram-positive multidrug-resistant pathogen, capable of releasing toxins and colonising the gut. C. difficile infections (CDI) lead to symptoms ranging from mild diarrhoea to toxic megacolon and pseudomembranous colitis and, in some severe cases, death. Recurrent CDI episodes are also a considerable issue and one of the main reasons for the burden on healthcare systems caused by C. difficile. Type IV pili (TFP) are protein filaments that extrude from bacterial cells and are found in Grampositive and Gram-negative pathogens. TFP have been shown to enhance virulence and described functions include bacterial motility, colonisation, biofilm formation and DNA up taking. In this work, genes in the primary cluster encoding TFP proteins, particularly PilA1, the major pilin composing TFP, and PilD1, one of the pre-pilin peptidases, and the minor pilin PilJ were studied in detail. Mutagenesis studies of PilA1, PilD1 and PilJ (a minor pilin) were performed and their role in C. difficile TFP biosynthesis, biofilm formation and motility was investigated. Interestingly, PilD1 and PilJ are not required in TFP biosynthesis in cell growth, unlike previous observations for other TFP, but PilD1 seems to be important on solid media. Surprisingly, flagella expression is affected in the mutants suggesting a potential crosstalk between twitching and swimming motility beyond c-di-GMP regulation. This work furthers current understanding of biological features of C. difficile TFP. It raises new research questions regarding the interplay between C. difficile TFP and flagella. Together, this provides a deeper understanding of mechanisms involved in CDI that could be explored as novel therapeutic targets.