Graduate Thesis Or Dissertation

 

Evolution of a streamlined cooperator in Pseudomonas aeruginosa quorum sensing Public Deposited

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  • Social behavior leading to the production of common goods is prone to exploitation. One such behavior in Pseudomonas aeruginosa is quorum sensing (QS), by which the bacteria produce signals to regulate extracellular common goods. Exploitation comes in the form of cheaters which have a mutation in the central quorum sensing regulator LasR. Previously we demonstrated that cheaters arise in vitro under conditions that require QS because they have a growth advantage over the wild-type. In the same experiment we also observed lasR mutants that produced select (QS) products. We initially hypothesized that this partially QS-proficient strain evolved from a QS-deficient ancestor and would harbor a second-site mutation. To understand the underlying molecular mechanism, the genomes of this strain and its wild type ancestor were sequenced. Two unique mutations were identified. Subsequent genetic analysis included complementation of candidate mutations and construction of respective mutants using evolved mutations. We found that the original mutation in lasR itself is sufficient to cause partial QS-proficiency. Because the mutation resides in the DNA binding domain of LasR, we predict that it alters promoter specificity, resulting in a reduction of the LasR regulon to the functions essential for in vitro growth. This streamlined cooperator will be an excellent model for the evolution of regulators and their specificity.
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