Identification and Regulation of a Novel Citrobacter rodentium Gut Colonization Fimbria (Gcf)

The Gram-negative enteric bacteriumCitrobacter rodentium is a natural mouse pathogen that has been extensively used as a surrogate model for studying the human pathogens enteropathogenic and enterohemorrhagicEscherichia coli . All three pathogens produce similar attaching and effacing (A/E) lesions in the intestinal epithelium. During infection, these bacteria employ surface structures called fimbriae to adhere and colonize the host intestinal epithelium. ForC. rodentium , the roles of only a small number of its genome-carried fimbrial operons have been evaluated. Here, we report the identification of a novelC. rodentium colonization factor, calledg utc olonizationf imbria (Gcf), which is encoded by a chaperone-usher fimbrial operon. AgcfA mutant shows a severe colonization defect within the first 10 days of infection. Thegcf promoter is not active inC. rodentium under severalin vitro growth conditions; however, it is readily expressed in aC. rodentium Δhns1 mutant lacking the closest ortholog of theEscherichia coli histone-like nucleoid structuring protein (H-NS) but not in mutants with deletion of the other four genes encoding H-NS homologs. H-NS binds to the regulatory region ofgcf , further supporting its direct role as a repressor of thegcf promoter that starts transcription 158 bp upstream of the start codon of its first open reading frame. Thegcf operon possesses interesting novel traits that open future opportunities to expand our knowledge of the structure, regulation, and function during infection of these important bacterial structures.IMPORTANCE Fimbriae are surface bacterial structures implicated in a variety of biological processes. Some have been shown to play a critical role during host colonization and thus in disease. Pathogenic bacteria possess the genetic information for an assortment of fimbriae, but their function and regulation and the interplay between them have not been studied in detail. This work provides new insights into the function and regulation of a novel fimbria called Gcf that is important for early establishment of a successful infection byC. rodentium in mice, despite being poorly expressed underin vitro growth conditions. This discovery offers an opportunity to better understand the individual role and the regulatory mechanisms controlling the expression of specific fimbrial operons that are critical during infection.