Acyl-Homoserine Lactone Quorum Signal Degradation by Soil and Clinical Pseudomonas sp.

Citation

Huang, Jean Jing (2007) Acyl-Homoserine Lactone Quorum Signal Degradation by Soil and Clinical Pseudomonas sp. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/fjr6-5f51. https://resolver.caltech.edu/CaltechETD:etd-04162007-092010

Abstract

Acyl-homoserine lactones (AHLs) are signaling molecules that are used by several species of <i>Proteobacteria</i> in a process of cell-to-cell communication known as quorum sensing. The production, secretion, and detection of these signaling molecules are used to regulate a variety of microbial group behaviors, such as motility, the production of extracellular enzymes, antibiotics, and virulence factors. This thesis describes the ability for two <i>Pseudomonas sp.</i>, a soil - isolate strain PAI-A and a clinical - isolate <i>Pseudomonas aeruginosa</i> strain PAO1, to degrade long chain acyl-homoserine lactone quorum signaling molecules, and explores the implications for this degradation activity. <i>P. aeruginosa</i> is an opportunistic pathogen that engages in quorum sensing with a long and a short chain AHL: 3OC12HSL and C4HSL and regulates the production of its virulence genes in this way. The soil isolate does not accumulate AHLs, and there is no evidence for its engagement in quorum sensing. Both species degrade long chain AHL via an acylase mechanism in which the molecule is cleaved at the amide bond. Two enzymes, PvdQ and QuiP, encoded by the genes PA2385 and PA1032 of <i>P. aeruginosa</i>, were found sufficient for the degradation of long chain AHL, but only the PA1032 gene is necessary for this process. PA1032 is transcribed and its protein product is present during degradation of long chain AHL. Studies of PAO1 lagless, a variant of <i>P. aeruginosa</i> that always degrades long chain AHL, indicate that this strain is broken in the regulation of PA1032. PAO1 lagless was found to express the PA1032 gene throughout planktonic and biofilm growth states, but wild type PAO1 expressed PA1032 locally in the center of biofilm microcolonies. This finding suggests PAO1 may use its ability to degrade one of its two AHLs during this dynamic growth state. Degenerate primers designed from PA1032 of PAO1 enabled the determination of a 2.5 kb putative AHL acylase of the soil isolate. Collectively, these studies of how <i>Pseudomonas</i> soil and clinical isolates degrade AHL suggest the diverse ways in which the degradation of acyl-homoserine lactone molecules may be used.

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