UBC Theses and Dissertations
The role of ColRS two-component regulatory system in rhizosphere colonization and tolerance to abiotic stress in Pseudomonas aeruginosa Zhang, Yue
Pseudomonas aeruginosa is a versatile bacterium found ubiquitously in the environment and is an opportunistic pathogen of diverse organisms, including animals and plants. A key determinant of bacterial adaptability is the ability to sense and respond appropriately to environmental stimuli. ColRS is a two-component regulatory system previously shown to be required for P. fluorescens colonization of plant roots (the “rhizosphere”) and P. aeruginosa virulence in C. elegans; however, the mechanisms by which ColRS regulates fitness in a host environment are unknown. I found that colR and colS deletion mutants in P. aeruginosa were significantly impaired in their ability to colonize the rhizosphere of Arabidopsis. In addition, we showed that colR in the P. aeruginosa cystic fibrosis epidemic isolate, LESB58, is required for virulence in a mouse abscess model. Using RNA-seq, I found a total of 128 genes that were dysregulated in the colR mutant in the rhizosphere, many of which have products that are predicted to localize to the cytoplasmic or outer membranes, suggesting ColRS may function in maintaining membrane integrity. Using P. aeruginosa transposon insertion mutants in colR-dependent genes, I identified novel genes required for rhizosphere colonization, including the protein tyrosine phosphatase tpbA, diacylglycerol kinase dgkA, and a type 2 phosphatidic acid phosphatase. Lastly, I showed that P. aeruginosa colR is required for tolerance to high levels of iron, zinc, and manganese, and for growth at acidic pH. Because functional analysis of rhizosphere gene expression showed that high iron concentration and low pH are stresses that may be present in the rhizosphere, the ColRS two-component system likely promotes P. aeruginosa colonization of the Arabidopsis rhizosphere through regulation of genes required to protect against these stresses.
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