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Title: Fatty acid signalling in Pseudomonas eruginosa
Author: Chen, Yu
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2014
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Fatty acid molecules play a crucial role in bacterial cell-cell communication. Recently the novel fatty acid messenger cw-2-decenoic acid (CDA) has been discovered in Pseudomonas aeruginosa culture supernatants. CDA belongs to the diffusible signal factor (DSF) family which consists of a series of fatty acid signal molecules. DSF-type signals are widespread among Gram-negative bacteria, such as DSF in Xanthomonas campestris pv. campestris and Burkholderia DSF (BDSF) in Burkholderia cenocepacia. DSF and BDSF are both synthesised via enoyl-CoA hydratases and are capable of modulating virulence factor production and controlling the switch between sessile biofilm and planktonic lifestyles. However, little is known about the synthesis and function of CDA in P. aeruginosa. This project is directed towards the discovery of the CDA synthase and the biological function of this signal molecule in P. aeruginsoa. The results obtained show that CDA inhibits biofilm formation, induces biofilm dispersal and has a global effect on both the Quorum Sensing (QS) regulatory systems (e.g. las and rhl), QS target genes (e.g. phz and lec) and the post-transcriptional rsm system. In both chemically defined and rich LB growth media, free amino acids stimulated CDA biosynthesis whereas it was reduced following mutation of the rhamnobpid biosynthetic genes rhl A and rhlC. The putative enoyl-CoA hydratase PA0744 was identified as a CDA synthase in P. aeruginosa. Mutation of the PA0744 gene resulted in a drastic reduction in CDA production, leading to the loss of CDA-induced phenotypes. However, PA0744 was not the only CDA synthase in P. aeruginosa because CDA still accumulated while PA0744 mutant was grown in the minimal medium. In addition, the putative enoyl-CoA hydratase, PA3426 (cbsA), was identified as a probable CDA-degrading enzyme. Overexpression of cbsA reduced the CDA production and promoted the transition between motility and sessility. Furthermore, CbsA exerted reciprocal control on the small RNAs RsmZ and RsmY via an as yet unknown extracellular signal(s). Multiple two-component systems including GacS/A, PhoQ/P and PmrB/A were also shown to be involved in the CbsA regulatory network in P. aeruginosa. In summary, this work reveals a new regulatory network controlling multiple target genes based on CDA which is synthesised via one or more enoyl-CoA hydratases.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available