High frequency genetic variation and osmotic stress survival in the success of the human pathogen Campylobacter jejuni

Campylobacter jejuni is the leading bacterial cause of severe infectious diarrhea worldwide, and prior infection with the pathogen is highly correlated with the acute neuromuscular paralysis of Guillain-Barré Syndrome. As a zoonotic bacterium, C. jejuni successfully colonizes multiple host animal species harmlessly, survives transmission in the natural environment, and as a widespread food-borne pathogen, causes gastroenteritis in humans. Stress survival mechanisms are important to understand because they enable this success, and may lead to new food safety strategies and interventions to eliminate the harm caused by C. jejuni. Here, the global response of C. jejuni to hyperosmotic stress—which is encountered in hosts, the environment, and food processing—was characterized by whole-genome transcriptional profiling. This identified important physiological responses to hyperosmotic stress, and in particular, identified the importance of cross-induction of heat shock and oxidative stress response proteins. Single-cell and single-colony comparisons also identified prevalent stress phenotypic heterogeneity within the population. Contributing to the phenotypic variation, high frequency multifarious mutations in two purine biosynthesis genes were identified via whole-genome sequencing of colonial isolates. These mutations differentially affected tolerance to a variety of stresses, and different mutations were important for enhanced intracellular survival in epithelial cells, which is correlated with virulence in humans. This genetic variation in the population also contributed to enhanced biofilm formation, and conferred differential niche-preference behavior to individual mutation-bearing bacteria. Together, these high frequency mutations contributed to novel adaptive properties of C. jejuni, and thus a mechanism of success was identified. A hyperosmotic stress-upregulated gene, cj1533c, was also recognized as a novel determinant of hyperosmotic and oxidative stress resistance. Preliminary characterizations of cj1533c via mutational and proteomic analyses suggested a critical role for Cj1533c, a putative ATPase, in the coordination of multiple stress-related cellular pathways. Lastly, new genetics tools, fluorescent probes, and proteomics techniques were adapted for used in future C. jejuni research. Collectively, a number of unique C. jejuni success mechanisms were identified via their importance for hyperosmotic stress tolerance.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat