Regulating Campylobacter jejuni flagellar gene expression: transcriptional and post-transcriptional mechanisms of control
The bacterial pathogen Campylobacter jejuni is the leading cause of foodborne gastroenteritis in the developed world. C. jejuni flagella are crucial virulence determinants, but the regulation of these complex organelles within different environments is not fully understood. Moreover, regulatory RNAs are important for virulence and flagellar gene expression in many prokaryotes, but their role in C. jejuni biology is unknown. The first aim was to understand flagellar regulation in acidic conditions and what effect this has on virulence. The most acidic pH C. jejuni was able to survive was pH 3.6 and acid-shock at this pH and pH 5 increased expression of a subset of flagellar genes and increased invasion of intestinal epithelial cells. The second aim of this study was to characterise the function of two paralogous small non-coding RNAs (less than 50 nucleotides), NC1 and NC4, which were identified in the C. jejuni NCTC11168 transcriptome and are predicted to regulate flagella gene expression. NC1 and NC4 expression was dependent on the flagellar sigma factor, sigma28, and post-transcriptionally regulated expression of predicted sigma54-dependent C. jejuni flagellar gene targets in an E. coli based GFP reporter system. However, microarray and phenotypic analysis showed no clear differences in gene expression between NC1/NC4 deletion and over-expression mutants compared to the wild-type strain. The conclusions are that flagellar gene expression is regulated by acidic conditions and C. jejuni invasion of intestinal epithelial cells may be primed in response to acid. In addition, the transcription of NC1 and NC4 is linked to flagella expression and they may function to post-transcriptionally regulate sigma54-dependent flagella genes in C. jejuni. Although the biological significance of NC1 and NC4 remains unknown, this is the first study to show that non-coding RNAs are potential regulators of gene expression in Campylobacter.
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