This thesis is missing page 53, no other copies have this page. -Digitization Centre / Bacterial adaptation to changing conditions and to the host environment requires coordinated changes in gene expression that permit more efficient utilization of metabolites and increased survival. An important form of gene control is through the use of alternative sigma factors that direct RNA polymerase to recognize a distinct group of genes. One such sigma factor is RpoS, which is widely present in Proteobacteria including many serious human pathogens. As a key stress response regulator, RpoS plays an important role in adaptation, but its effect on virulence varies in different species. RpoS contributes to virulence through either enhancing survival against host defense systems or directly regulating expression of virulence factors in some pathogens, while RpoS is dispensable, or even inhibitory, to virulence in others. The primary objective of this study is to understand the mechanism of RpoS control in gene expression and pathogenesis of Escherichia coli. This thesis first describes the characterization of RpoS regulon in laboratory and pathogenic E. coli strains by transcriptome profiling analysis. Comparison of RpoS regulons identifies a core set of RpoS-controlled genes as well as strain-specific groups of genes, including many implicated in virulence. The contribution of RpoS to enteropathogenesis in vivo was tested using a Citrobacter rodentium (CR)mouse infection model that is commonly used to simulate E. coli infection in human intestine. Mutations in rpoS result in reduced colonization and delay in mortality, indicating RpoS is important for full virulence. Clinical and natural E. coli isolates exhibit variable abilities in stress resistance and virulence, which is partly attributable to attenuating polymorphisms of rpoS commonly found in E. coli populations. A possible mechanism responsible for the occurrence of rpoS polymorphisms in pathogenic E. coli is addressed. Using a group of representative enterohemorrhagic E. coli strains, we report that growth-enhanced mutants can be selected during growth on succinate and other poor carbon sources under both aerobic and anaerobic conditions. The majority of these mutants carry nonsense or missense mutations in rpoS. Phenotypic microarray analysis reveals that rpoS mutations result in increased utilization of 92 nitrogen and 8 carbon sources. Therefore, the occurrence of rpoS polymorphisms may increase the fitness of the population as a whole for better nutrient scavenging. In conclusion, RpoS may be viewed as a transient regulator that orchestrates the temporal expression of a large regulon for better adaptation under specific conditions including natural and host environments. Under conditions not requiring RpoS, its functions can be turned off through decreasing expression, rapid proteolysis, inhibition of RpoS activity, or selection of attenuating mutations. The final part of this thesis reviews the distinct and niche-dependent involvement of RpoS in virulence of many rpoS-bearing pathogens.
- / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/24448 |
| Date | 01 1900 |
| Creators | Dong, Tao |
| Contributors | Schellhorn, Herb, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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