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Evidence that a partner-switching regulatory system modulates hormogonium motility in the filamentous cyanobacterium Nostoc punctiforme
Date of Award
Master of Science (M.S.)
Douglas D. Risser
First Committee Member
Craig A. Vierra
Second Committee Member
Douglas C. Weiser
Partner-switching regulatory systems (PSRSs) are utilized by many different bacteria to regulate a wide array of cellular responses, from stress response to expression of virulence factors. The filamentous cyanobacterium Nostoc punctiforme can transiently differentiate motile filaments, called hormogonia, in response to various changes in the environment. Hormogonia utilize a Type IV pilus (T4P) complex in conjunction with a secreted polysaccharide for gliding motility along solid surfaces. This study identified three genes, designated hmpU, hmpW, and hmpV, encoding the protein components of a PSRS involved in regulation of hormogonium motility in N. punctiforme. Although mutant strains with in-frame deletions in hmpU, hmpW, and hmpV differentiated morphologically distinct hormogonium-like filaments, further phenotypic analysis demonstrated significant distinctions among the strains. The ∆hmpW strain contained a higher percentage of motile filaments that moved faster than the wild-type strain, while the ∆hmpU and ∆hmpV strains consisted of fewer motile filaments that moved at a slower rate compared to wild type. Immunoblotting and immunofluorescence of PilA, the major component of the pilus in the T4P system, showed that although all mutant strains appeared to express similar levels of PilA protein, the ∆hmpU and ∆hmpV strains displayed reduced extracellular PilA. Lectin blotting and staining with fluorescently-labeled UEA lectin demonstrated a decrease in extracellular hormogonium polysaccharide in the ∆hmpU and ∆hmpV strains, consistent with the current understanding that the polysaccharide is secreted via the T4P system. Epistasis analysis demonstrated that the ∆hmpW, ∆hmpV double-deletion mutant strain displayed reduced spreading in plate motility assays, similar to the ∆hmpV single mutant. Together, these results support a model in which the HmpU phosphatase and HmpW serine kinase control the phosphorylation state of the HmpV protein, modulating its activity on a downstream target to ultimately promote activation of the T4P motor complex and enhance hormogonium motility.
Riley, Kelsey Wynne. (2018). Evidence that a partner-switching regulatory system modulates hormogonium motility in the filamentous cyanobacterium Nostoc punctiforme. University of the Pacific, Thesis. https://scholarlycommons.pacific.edu/uop_etds/3135