Regulation of Virulence in the Human Pathogen Campylobacter jejuni by the RNA Binding Protein CsrA

Abstract

Campylobacter jejuni is a leading bacterial cause of gastroenteritis in both the industrialized and developing world and has been associated with the onset of long term, debilitating sequelae such as Guillain-Barre Syndrome and reactive arthritis. The RNA binding protein CsrA (carbon storage regulator A), one of the relatively few regulatory elements in the C. jejuni genome, has been shown to regulate a number of processes in several other bacterial species including metabolism and virulence characteristics. We proposed the hypothesis that CsrA globally regulates C. jejuni pathogenesis via post-transcriptional repression or activation of virulence associated proteins. We created a csrA mutant in the C. jejuni strain 81-176 to investigate the role of CsrA in the virulence and physiology of the organism. In the absence of CsrA, we found that C. jejuni was no longer able to resist oxidative stresses, form biofilms, or adhere to intestinal epithelial cells in vitro in comparison to the wild type. We also found that C. jejuni was less motile than its parent strain and was defective in autoagglutination and fibronectin binding in vitro and mouse colonization in vivo. When we compared the proteome of the mutant strain to that of the wild type, we found that CsrA acted mostly upon the expression of proteins in stationary phase. In the absence of CsrA proteins responsible for various steps in C. jejuni metabolism, motility, oxidative stress responses, and epithelial cell adherence were differentially expressed. Finally, to further understand the molecular mechanisms of C. jejuni CsrA, we expressed it in a csrA mutant strain of E. coli. By heterologously expressing the C. jejuni protein in strain in which CsrA had been thoroughly characterized, we were able to show by complementation that C. jejuni CsrA was capable of both activating and repressing known targets of E. coli CsrA indicating that the molecular mechanisms of the two proteins are inherently the same.