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Title: Dynamics, formation and segregation of the cytoplasmic chemoreceptor cluster in Rhodobacter sphaeroides
Author: Jones, Christopher William
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2013
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The internal organisation of bacteria is far more complex than originally thought. Many components of the cell have specific localisation patterns. Proteins are localised to many different regions of the cell by numerous mechanisms, and often their function depends on correct localisation. Bacterial and plasmid DNA are also highly organised and actively positioned. These tightly regulated positioning patterns ensure stable maintenance of genetic material. Members of the ParA/MinD family of ATPases are responsible for the segregation of a large number of bacterial chromosomes and plasmids. Recently members of this family have been shown to position and segregate protein complexes. One such complex is the cytoplasmic chemosensory cluster of Rhodobacter sphaeroides. This large complexes are segregated from a single cluster positioned at the mid-cell to two clusters at 1/4, 3/4 positions by the ParA homologue PpfA using the nucleoid as a scaffold. This ensures that each daughter cell inherits a cluster. This study sought to investigate this cytoplasmic chemosensory cluster, and its positioning and segregation by PpfA through the cell cycle. The use of fluorescence recovery after photobleaching revealed that like membrane bound chemoreceptor arrays the cytoplasmic cluster of R. sphaeroides is a highly stable complex. The difference seen between the cytoplasmic cluster and the data reported for the membrane bound cluster of Escherichia coli is probably due to the lack of membrane helping hold the array together. Investigation of the role of PpfA in segregation of the cytoplasmic cluster, using fluorescence imaging and single molecule tracking with a range of mutants through the cell cycle, suggest that it uses a mechanism unlike any reported for ParA homologues. Single molecule tracking of PpfA molecules shows that the chemoreceptor TlpT stabilises PpfA molecules resulting in slower diffusion of PpfA molecules at the cluster. The use of a ΔppfA mutant shows that PpfA restrains the movement of the cluster, together these results suggest a model in which TlpT stabilises PpfA’s interaction with the nucleoid and PpfA positions the cluster.
Supervisor: Judith, Armitage Sponsor: BBSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry ; Microbiology ; Rhodobacter sphaeroides ; Chemotaxis ; Chemoreceptors