Mechanisms and roles of the LuxS system, methyl recycling, and DNA methylation on the physiology of Campylobacter jejuni

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2015-01-01
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Mou, Kathy
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Paul J. Plummer
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Veterinary Microbiology and Preventive Medicine
Our faculty promote the understanding of causes of infectious disease in animals and the mechanisms by which diseases develop at the organismal, cellular and molecular levels. Veterinary microbiology also includes research on the interaction of pathogenic and symbiotic microbes with their hosts and the host response to infection.
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Campylobacter jejuni is one of the leading causes of human bacterial gastroenteritis, and campylobacteriosis in sheep. The genetic diversity of this organism, the potential for multiple sources to transmit C. jejuni to humans, and the possession of a variety of virulence factors and antimicrobial resistance mechanisms make C. jejuni a serious health problem worldwide. The autoinducer-2 (AI-2)/LuxS system has been the focus of several studies for its potential applications to attenuate C. jejuni virulence. A study from our group found that the LuxS enzyme plays a critical role in virulence and fitness of C. jejuni IA3902 and 11168 strains. Mutagenesis of the luxS gene negatively impacted C. jejuni colonization of the gastrointestinal tract of several host species. However, the physiologic basis for this colonization defect is unclear. In addition to AI-2 production, LuxS is also a key enzyme involved in the activated methyl cycle (AMC). The AMC is an important source for the formation of S-adenosylmethionine, a methyl donor crucial to biological processes like DNA methylation. DNA methylation has also been linked with a diverse number of important physiological and pathogenic mechanisms in many bacteria, but is poorly understood in C. jejuni. The collective work from this thesis attempts to address some of the knowledge gaps on the role of LuxS, methyl recycling, and DNA methylation in C. jejuni physiology. Collectively, results from our study showed that luxS mutation interrupted the AMC resulting in significant changes to intracellular concentrations of several key metabolites. However, the colonization-associated factors tested on our luxS mutants in this thesis do not show evidence of being the primary mechanisms responsible for the luxS mutant's decreased colonization ability. We proceeded to analyze the role of LuxS on DNA methylation and found that the luxS mutation had no appreciable effect on the methylome profile of the mutant. We also compared the methylome profiles of three important C. jejuni strains and found significant strain variability in the methylomes, which suggest a potential role for DNA methylation in Campylobacter pathobiology. The methylome studies also revealed a novel putative methyltransferase which we later confirmed and definitively assigned to a specific methylation motif. While mutagenesis of the methyltransferase gene resulted in a loss of methylation of its cognate motif we were unable to show an effect on the growth or motility phenotypes tested in our study. In summary, the luxS mutation demonstrated physiological effects on the AMC, but the colonization mechanisms affected by the mutation are still unknown. However, DNA methylation studies revealed strain-specific methylation profiles, including a unique methyltransferase, which may serve a biological and/or pathogenic purpose specific to the strain.

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Thu Jan 01 00:00:00 UTC 2015