Date of Award

May 2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Sonia L. Bardy

Committee Members

Steven A. Forst, Mark J. McBride, Charles F. Wimpee, Ching-Hong Yang

Keywords

Biofilm, Chemotaxis, Motility, Partitioning, Pseudomonas

Abstract

Bacterial chemotaxis is the movement of a cell towards an attractant or away from a repellent. This controlled movement is possible due to the chemotaxis system, which is typically made up of several proteins that collectively sense the stimuli and transduce the signal within the cell to mediate a motility response. The chemotaxis proteins of Pseudomonas aeruginosa are encoded in two clusters, which are located at different regions of the chromosome: che I and che V. These gene clusters are known to control chemotaxis via swimming, or flagellar-based, motility. When expressed, these chemotaxis proteins associate with each other to form tight clusters that are composed of thousands of copies of each protein. These clusters localize to the flagellated pole in young cells and show bi-polar localization in older cells. Within cluster che I are genes encoding two Par-like proteins: ParC and ParP. Both Par-like proteins are needed for wild type swimming motility, yet ParP appears to have a more important role as its loss results in a greater swimming defect. Cluster formation of the chemotaxis histidine kinase CheA was reduced by 50% in the absence of either Par-like protein, thus demonstrating a potential mechanism behind the reduced swimming motility. However, the equivalent reduction in foci formation does not explain the larger defect resulting from the absence of ParP. ParC has a predicted ATPase domain and mutation of the ATP binding site resulted in a dominant negative swimming phenotype when expressed in trans. ParP has a CheW-like domain and overexpression of CheW can partially restore swimming motility to a parP mutant. Bacterial two-hybrid results showed that the Par-like proteins interact with each other and the chemotaxis system, and that ParP interacts with DipA, a phosphodiesterase which degrades cyclic-di-GMP and is important for biofilm dispersion and chemotaxis. Deletion of dipA resulted in a similar defect in swimming motility as the parP mutant. Surface flagellin levels were slightly increased in both the parP and dipA mutants, although it is not known if this was due to increased flagellation or longer flagella. Fluorescence microscopy results showed that ParP has an interdependence in polar cluster formation with both CheA and DipA. CheA cluster formation is dependent on ParC. Due to the direct interactions and interdependence of cluster formation of ParP and DipA, and the fact that parP and dipA mutants have similar defects in swimming motility and increases in surface flagellin levels, further investigation into the role of ParP in biofilm dispersion is warranted.

Available for download on Thursday, May 30, 2019

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