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Evolutionary adaptation of an AraC-like regulatory protein in Citrobacter rodentium and Escherichia species.

ABSTRACT: The evolution of pathogenic bacteria is a multifaceted and complex process, which is strongly influenced by the horizontal acquisition of genetic elements and their subsequent expression in their new hosts. A well-studied example is the RegA regulon of the enteric pathogen Citrobacter rodentium. The RegA regulatory protein is a member of the AraC/XylS superfamily, which coordinates the expression of a gene repertoire that is necessary for full pathogenicity of this murine pathogen. Upon stimulation by an exogenous, gut-associated signal, namely, bicarbonate ions, RegA activates the expression of a series of genes, including virulence factors, such as autotransporters, fimbriae, a dispersin-like protein, and the grlRA operon on the locus of enterocyte effacement pathogenicity island. Interestingly, the genes encoding RegA homologues are distributed across the genus Escherichia, encompassing pathogenic and nonpathogenic subtypes. In this study, we carried out a series of bioinformatic, transcriptional, and functional analyses of the RegA regulons of these bacteria. Our results demonstrated that regA has been horizontally transferred to Escherichia spp. and C. rodentium. Comparative studies of two RegA homologues, namely, those from C. rodentium and E. coli SMS-3-5, a multiresistant environmental strain of E. coli, showed that the two regulators acted similarly in vitro but differed in terms of their abilities to activate the virulence of C. rodentium in vivo, which evidently was due to their differential activation of grlRA. Our data indicate that RegA from C. rodentium has strain-specific adaptations that facilitate infection of its murine host. These findings shed new light on the development of virulence by C. rodentium and on the evolution of virulence-regulatory genes of bacterial pathogens in general.

SUBMITTER: Tan A

PROVIDER: S-EPMC4363417 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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Evolutionary adaptation of an AraC-like regulatory protein in Citrobacter rodentium and Escherichia species.

Tan Aimee A Petty Nicola K NK Hocking Dianna D Bennett-Wood Vicki V Wakefield Matthew M Praszkier Judyta J Tauschek Marija M Yang Ji J Robins-Browne Roy R

Infection and immunity 20150126 4

The evolution of pathogenic bacteria is a multifaceted and complex process, which is strongly influenced by the horizontal acquisition of genetic elements and their subsequent expression in their new hosts. A well-studied example is the RegA regulon of the enteric pathogen Citrobacter rodentium. The RegA regulatory protein is a member of the AraC/XylS superfamily, which coordinates the expression of a gene repertoire that is necessary for full pathogenicity of this murine pathogen. Upon stimulat ...[more]

PMID: 25624355

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Project description:The gut microbiota plays a crucial role in susceptibility to enteric pathogens, including Citrobacter rodentium, a model extracellular mouse pathogen that colonizes the colonic mucosa. C. rodentium infection outcomes vary between mouse strains, with C57BL/6 and C3H/HeN mice clearing and succumbing to the infection, respectively. Kanamycin (Kan) treatment at the peak of C57BL/6 mouse infection with Kan-resistant C. rodentium resulted in relocalization of the pathogen from the colonic mucosa and cecum to solely the cecal luminal contents; cessation of the Kan treatment resulted in rapid clearance of the pathogen. We now show that in C3H/HeN mice, following Kan-induced displacement of C. rodentium to the cecum, the pathogen stably colonizes the cecal lumens of 65% of the mice in the absence of continued antibiotic treatment, a phenomenon that we term antibiotic-induced bacterial commensalization (AIBC). AIBC C. rodentium was well tolerated by the host, which showed few signs of inflammation; passaged AIBC C. rodentium robustly infected naive C3H/HeN mice, suggesting that the AIBC state is transient and did not select for genetically avirulent C. rodentium mutants. Following withdrawal of antibiotic treatment, 35% of C3H/HeN mice were able to prevent C. rodentium commensalization in the gut lumen. These mice presented a bloom of a commensal species, Citrobacter amalonaticus, which inhibited the growth of C. rodentium in vitro in a contact-dependent manner and the luminal growth of AIBC C. rodentium in vivo. Overall, our data suggest that commensal species can confer colonization resistance to closely related pathogenic species. IMPORTANCE Gut bacterial infections involve three-way interactions between virulence factors, the host immune responses, and the microbiome. While the microbiome erects colonization resistance barriers, pathogens employ virulence factors to overcome them. Treating mice infected with kanamycin-resistant Citrobacter rodentium with kanamycin caused displacement of the pathogen from the colonic mucosa to the cecal lumen. Following withdrawal of the kanamycin treatment, 65% of the mice were persistently colonized by C. rodentium, which seemed to downregulate virulence factor expression. In this model of luminal gut colonization, 35% of mice were refractory to stable C. rodentium colonization, suggesting that their microbiotas were able to confer colonization resistance. We identify a commensal bacterium of the Citrobacter genus, C. amalonaticus, which inhibits C. rodentium growth in vitro and in vivo. These results show that the line separating commensal and pathogenic lifestyles is thin and multifactorial and that commensals may play a major role in combating enteric infection.

Dataset Information

Evolutionary adaptation of an AraC-like regulatory protein in Citrobacter rodentium and Escherichia species.

Publications

Evolutionary adaptation of an AraC-like regulatory protein in Citrobacter rodentium and Escherichia species.

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