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Title: The ecological implications for combinatorial signalling in Pseudomonas aeruginosa
Author: Gurney, James Ryan
ISNI:       0000 0004 6352 9147
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2014
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In recent years it has been acknowledged that bacteria engage in a number of diverse social behaviours. An large body of research has focused on the influence that Quorum sensing (QS) has on these behaviours. The majority of this work has traditionally focused on a mechanistic understanding of how QS-dependent genes are regulated, and how this regulation affects cell-cell communication. In contrast, relatively few papers have focused on the functional role that QS provides to bacteria. This has led to confusion, and a number of attempts to unify the process under a functional argument. Correctly understanding the functional role of QS will help inform diverse fields of research ranging from medical to industrial. To help address this, this study focused on three major questions: (i) What is the value to bacteria for releasing and responding to more than one signal molecule? Are bacteria capable of combining the information from more than one signal to resolve the conflation between environmental factors and population density? (ii) Are private goods capable of maintaining cooperation in a long term selection environment in which a second signal molecule has no role in the metabolism of those private goods? (iii) Is a long term selection experiment that gives combinatorial strains a higher relative fitness capable of selecting for the use of non-cognate signal molecules which are involved in the acquisition of public goods? Once a increased affinity for the non-cognate molecule is achieved are the new isolates capable of Kin discrimination? In this thesis it is shown that the opportunistic pathogen Pseudomonas aeruginosa uses a combination of signal molecules to control gene expression and the production of public goods. A number of these products are controlled in a differential manner to non-secreted products. This lends support to the hypothesis of combinatorial signalling. Using a long term selection experiment in which strains were cycled between a private and public goods medium. P. aeruginosa isolates that were capable of cheating on the ancestor strain emerged. These isolates seemed to rely on the production of public goods via a combinatorial signalling process. These isolates had a higher relative fitness in a QS-dependent media with the addition of both signals; when compared to the ancestor. Finally, using a similar long term selection experiment in an attempt to evolve a better response to a non-cognate signal molecule showed that under the conditions provided bacteria did not show a clear example of a cognate switch to the non-cognate signal molecule. Without a cognate switch experimentation into discrimination could not proceed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available