Doctoral Dissertations

Date of Award

5-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Chris D. Cox

Committee Members

Michael L. Simpson, Bruce Robinson, Alice C. Layton

Abstract

Quorum sensing is a mechanism by which bacteria can sense the levels of signaling molecules and respond by controlling the expression of target genes. The marine bacterium, Vibrio fischeri, has been extensively studied as a model for the quorum sensing mechanism in Gram-negative bacteria. In order to systematically investigate the quorum sensing regulatory network in V. fischeri, a conceptual model was first established based on the existing knowledge. Next, molecular microbiology and bioinformatics techniques were employed to both qualitatively and quantitatively characterize the system. These techniques included the quantification of the 3-oxo-C6-HSL concentrations in the cell culture supernatant using a bioluminescent bioreporter strain of E. coli, the measurements of the messenger RNA levels of quorum sensing genes (luxI, luxR, ainS and litR) using the reverse transcription-polymerase chain reaction (RT-PCR), as well as the sequence analysis of the promoter regions of quorum sensing related genes. A mathematical model composed of ordinary differential equations was created to characterize the regulatory process. The simulated annealing method was used to minimize the weighted discrepancy between the modeling output and the experimental data with correlations ranging from 0.85 to 0.99. This study, mathematically modeled the comprehensive quorum sensing regulatory system, which encompasses 3-oxo-C6-HSL, lux operon (luxR and luxICDABEG), C8-HSL, ainS, ainR, luxO, and litR, and can benefit the understanding of dozens of similar quorum sensing regulatory systems.

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