Control of virulence and physiology by the flagellin homeostasis checkpoint FliC-FliW-CsrA in the absence of motility.

UNLABELLED

Mutations affecting flagellin (FliC) have been shown to be hypervirulent in animal models and display increased toxin production and alterations in central metabolism. The regulation of flagellin levels in bacteria is governed by a tripartite regulatory network involving , , and , which creates a feedback system to regulate flagella production. Through genomic analysis of clade 5 strains (non-motile), we identified they have jettisoned many of the genes required for flagellum biosynthesis yet retain the major flagellin gene and regulatory gene . We therefore investigated the roles of , , and in the clade 5 ribotype 078 strain 1015, which lacks flagella and is non-motile. Analysis of mutations in , , and (and all combinations) on pathogenesis indicated that FliW plays a central role in virulence as animals infected with strains carrying a deletion of showed decreased survival and increased disease severity. These findings were supported by studies showing that mutations impacting the activity of FliW showed increased toxin production. We further identified that FliW can interact with the toxin-positive regulator TcdR, indicating that modulation of toxin production via FliW occurs by sequestering TcdR from activating toxin transcription. Furthermore, disruption of the network results in significant changes in carbon source utilization and sporulation. This work highlights that key proteins involved in flagellar biosynthesis retain their regulatory roles in pathogenesis and physiology independent of their functions in motility.

IMPORTANCE

is a leading cause of nosocomial antibiotic-associated diarrhea in developed countries with many known virulence factors. In several pathogens, motility and virulence are intimately linked by regulatory networks that allow coordination of these processes in pathogenesis and physiology. Regulation of toxin production by FliC has been demonstrated and and has been proposed to link motility and virulence. Here, we show that clinically important, non-motile strains have conserved FliC and regulatory partners FliW and CsrA, despite lacking the rest of the machinery to produce functional flagella. Our work highlights a novel role for flagellin outside of its role in motility and FliW in the pathogenesis and physiology of .