Date of Award

2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Microbiology and Immunology

First Advisor

Microbiology

Second Advisor

Copyright © 2014 Valerie Ray

Third Advisor

Doctor of Philosophy (PhD)

Abstract

Biofilm formation by bacteria provides them with a means to survive harsh environmental conditions and promote colonization of a particular surface (biotic or abiotic). Due to the resistance properties of biofilms, biofilm-forming bacteria are difficult to treat in the context of host infections. Thus, investigating the processes that control biofilm formation will promote the development of novel therapeutics. To study biofilm formation in the context of a host, I utilized as a model system the marine bacterium Vibrio fischeri, which must be competent to form a biofilm to colonize its squid host Euprymna scolopes. Biofilm formation by V. fischeri requires the syp polysaccharide locus, as well as the sensor kinase RscS and the response regulators SypG, required for syp transcription, and SypE, a negative regulator of biofilm formation. However, I predicted that other factors were also involved in biofilm formation. Therefore, my dissertation work focused on identifying novel factors involved in this process.

I first performed random transposon mutagenesis on a biofilm-competent strain of V. fischeri and screened for colonies that exhibited defects in wrinkled colony formation, a biofilm phenotype. This analysis permitted the identification of members of the Lux luminescence pathway (LuxQ and LuxU) as regulators of biofilm formation. Overall, my data support a model in which the Lux pathway bifurcates at LuxU to regulate biofilm formation through SypG.

Next, I shifted my focus to better understand SypG and its regulon. I asked whether this regulator was the direct transcriptional activator of the syp locus. I found that SypG recognizes and binds to a predicted enhancer sequence to promote syp transcription. Additionally, I identified three new putative members of the SypG regulon. The bam genes are involved in biofilm maturation and, at least, BamA is a secreted product, while the bal genes are involved in regulation of bioluminescence. Thus, the work from my dissertation: 1) identified novel factors involved in biofilm formation, 2) filled in critical gaps in our understanding of how the syp locus is regulated, 3) identified the first matrix protein in V. fischeri, and 4) provided new information regarding the control of cellular bioluminescence.

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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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