Investigation of novel gene regulatory mechanisms in the enteric pathogen Campylobacter jejuni

UoM administered thesis: Phd

  • Authors:
  • Nader Masri

Abstract

Campylobacter jejuni is the leading cause of bacterial gastroenteritis worldwide. While usually self-limiting, C. jejuni infections can lead to serious neurological sequelae in some patients. This highly variable organism lacks a number of classical gene regulatory mechanisms found in other bacterial pathogens. Three different gene regulatory mechanisms were investigated in this study: a temperature-responsive RNA regulator, translational read-through of frameshift mutations, and phase variation at simple sequence repeats. C. jejuni experiences different environments in the avian and human hosts, and during transmission. Some bacterial pathogens control expression of virulence genes through an RNA thermometer which senses a shift in temperature upon entry into a host. In the first study, a putative RNA secondary structure in the 5′-untranslated region of cj1163c was shown to thermoregulate expression of downstream genes. It was also shown, for the first time, that cj1163c is essential for zinc resistance. These novel data reveal a previously uncharacterised regulatory mechanism that controls expression of a putative zinc exporter in a temperature-dependent manner, which suggests a role for zinc resistance in virulence. The second study investigated read-through mechanisms of frameshift mutations in a pseudogene. Pseudogenes are remnants of once functional genes and their persistence in bacteria could be due to residual function. The glycerol-3-phosphate transporter gene (glpT) is disrupted in most C. jejuni strains, however, it was demonstrated that inactivation of the intact glpT increases fosfomycin resistance in strain 81116. In NCTC 11168, glpT is disrupted by two frameshift mutations. Point mutations in glpT frameshift regions fused to a reporter indicate a role for translation re-initiation in read-through of in-frame stop codons. Lastly, phase variation by slipped-strand mispairing at simple sequence repeats was investigated. These repeats are a common feature in lipooligosaccharide (LOS) biosynthesis genes. The LOS is involved in the pathogenesis of Guillain-Barré syndrome. In an attempt to characterise a potentially phase-variable LOS biosynthesis gene, cj1144c, in-frame homologues were inactivated in different strains, but this did not alter LOS electrophoretic mobility. This result was presumably confounded by the variation of other phase-variable LOS genes. These findings provide insight into novel regulatory mechanisms employed by this important human pathogen.

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Original languageEnglish
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Award date1 Aug 2018