Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599189
Title: Expression of flagella and haemolysin during swarming differentiation of P. mirabilis
Author: Fraser, G. M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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Abstract:
A motile but non-swarming transposon mutant of P. mirabilis was phenotypically characterised and found to be defective in cell elongation and hyperexpression of cell surface flagella and HpmA toxin. The transposon had inserted into the 441bp flgN, a flagella gene of undefined function, cotranscribed in an operon with the Class 3 anti-σ28 gene flgM. Flagella gene transcription was however not compromised in the mutant and as Class 3 genes were not strongly downregulated by FlgM feedback, the defect did not appear to lie in the membrane export machinery. Loss of FlgN reduced incorporation of flagellin into the membrane and caused release of unpolymerised FliC into the extracellular medium. The data suggest that FlgN facilitates acquisition of flagellin into filaments, a role that may be especially critical in attaining the threshold level of flagella required for swarming. Proteus FlgN was found to have leucine zipper-like motifs arranged on potential amphipathic helices, a feature conserved in cytosolic chaperones for the exported substrates of flagella-related type III virulence export systems. Expression of HpmA was investigated in wildtype P. mirabilis and in the flgN and FlhA flagellar gene mutants, both of which exhibit reduced swarm-specific haemolytic activity. Primer extension analysis of hpmBA genes revealed a differentially regulated σ70 promoter upstream of hpmB and several potential transcription initiation or RNA processing sites upstream of hpmA. Northern blot analyses of full length, truncated and deleted transcripts indicated processing of the unstable full length hpmBA transcript to yield a stable hpmA transcript. Transcriptional fusions of hpmB and hpmA to the luxAB reporter genes strengthened the view that swarm-specific regulation of transcription initiation was centred on the region 5' of hpmB, and involved sequences 5' of the σ70 promoter. The fusion analyses also indicated that repression of hpmBA transcription in the flagellar mutants could be relieved by truncation of the hpmB upstream region.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.599189  DOI: Not available
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