Identification of quorum sensing repressors in the squid light organ symbiont Vibrio fischeri
Quorum sensing describes the process by which bacteria coordinate certain group behaviors using cell densities. The marine bacterium Vibrio fischeri uses the canonical LuxI-LuxR quorum sensing system to regulate luminescence within its natural squid host, Euprymna scolopes. Because bioluminescence outside of the squid host is inefficient and costly, we hypothesized that quorum sensing is repressed while V. fischeri is outside of the host. A transcriptional reporter for the quorum sensing regulated protein QsrP was introduced into a V. fischeri transposon-mutant library to screen for mutants with altered qsrP expression. Of the 120,000 colonies screened, 25 mutant strains with increased qsrP expression levels were isolated and sequenced to determine the location of the transposon in the V. fischeri genome. Sequencing results of 20 strains returned thirteen unique insertions located in five different genes. To test whether the mutations affect the quorum sensing network, qsrP expression and luminescence of each mutant were measured in response to exogenous N-3-oxohexanoyl-homoserine lactone, the signaling molecule synthesized by LuxI. The mutant strains showed increased qsrP expression and luminescence when compared with the wild-type. qsrP in V. fischeri was also studied inside of the squid using confocal microscopy. Results showed comparable levels of qsrP expression for the wild-type and mutant strains inside the squid light organ, indicating that the repression of quorum sensing observed in culture is removed when V. fischeri is inside of the host. Taken together, this data suggests that V. fischeri has evolved several ways to repress quorum sensing while outside of the host environment.
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|Work Title||Identification of quorum sensing repressors in the squid light organ symbiont Vibrio fischeri|
|Subtitle||Eberly College of Science: Science Research Distinction Undergraduate Certificate Program (SCIRES) Thesis|
|License||Attribution-NonCommercial-NoDerivs 3.0 United States|
|Publication Date||Spring 2015|
|Deposited||June 22, 2016|
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