The Rho-independent transcription terminator for the porA gene enhances expression of the major outer membrane protein and Campylobacter jejuni virulence in abortion induction

Abstract

<p><em>Campylobacter jejuni</em> is a leading cause of foodborne illnesses worldwide. Its <em>porA</em> gene encodes the major outer membrane protein (MOMP) that is abundantly expressed and has important physiological functions including a key role in systemic infection and abortion induction in pregnant animals. Despite the importance of <em>porA</em> in <em>C. jejuni</em> pathogenesis, mechanisms modulating its expression levels remain elusive. At the 3 prime end of the <em>porA</em> transcript, there is a Rho-independent transcription terminator (named T<em>porA</em> in this study). Whether T<em>porA</em> affects the expression and function of MOMP remains unknown and is investigated in this study. Green fluorescent protein (GFP) fusion constructs with the <em>porA</em> promoter at the 5 prime end and an intact T<em>porA</em> or no T<em>porA</em> at the 3 feet end of the <em>gfp</em> coding sequence revealed that both transcript level of <em>gfp</em> and its fluorescence signals were more than 2-fold higher in the construct with T<em>porA</em> than the one without T<em>porA</em>. qRT-PCR analysis of the <em>porA</em> mRNA and immunoblotting detection of the MOMP protein in <em>C. jejuni</em> showed that disruption of T<em>porA</em> significantly reduced the <em>porA</em> transcript level and expression of the MOMP protein. mRNA decay assay demonstrated that disruption of T<em>porA</em> resulted in shortened transcript half-life of the upstream <em>gfp</em> or <em>porA</em> genes, indicating T<em>porA</em> enhances mRNA stability. In the guinea pig model, the <em>C. jejuni</em> construct with an interrupted T<em>porA</em> was significantly attenuated in abortion induction. Together these results indicate that T<em>porA</em> enhances the expression level of MOMP by stabilizing its mRNA and influences the virulence of <em>C. jejuni</em>.</p>