SYSTEMATIC INVESTIGATION OF QUORUM SENSING IN Escherichia coli

Title of Document: S Y S T E M A T I C I N V E S T I G A T I O N O F QUORUM SENSING IN Escherichia coli JUN LI, Doctor of Philosophy, 2007 Directed By: Professor, William E Bentley, Chemical and Biomolecular Engineering High throughput techniques and advanced mathematical tools have enabled systematic investigations of biological systems with unparalleled precision. Not only molecular interactions between components but mechanisms and the dynamic behaviors associated with these systems are revealed, suggesting that comprehensive systems biology can be realized in the near future. Quorum sensing, especially the auto-inducer2 (AI-2) system, has been extensively studied due to its commonality among bacteria and connections to pathogenic phenotypes. In this study, the E. coli quorum sensing AI-2 system was studied combing system-based mathematical modeling and high throughput genomic profiling. First, a Stochastic Petri Network (SPN) model was constructed based on available regulatory information. Simulations together with experimental data demonstrated that the apparent stimulation of AI-2 in the presence of glucose is not from the increased transcriptional or translational expression of AI-2 synthases luxS and pfs, nor from the increased metabolic flux associated with LuxS-related pathways but from an alternative AI-2 synthesis pathway. The conversion of adenosine with cellular extracts from both luxS and pfs mutants validated our prediction about the existence of an alternative non-LuxS related AI-2 synthesis pathway. Second, AI-2 uptake regulatory network was investigated in detail: lsrR-lacZ, lsrK-lacZ fusion reporters were constructed and the analysis found that lsrR is subject to its own repression and is induced by both lsrK and luxS. Further transcriptome analysis demonstrated that lsrR and lsrK, together with quorum signal AI-2, coregulate lsrRK regulon, which influences phenotypes (biofilm, small RNAs). Importantly, this regulation is in a distinctly different manner than that mediating the lsr operon. We hypothesize that lsrR acts together with AI-2 to mediate cellular processes and that the phosphorylation of AI-2 molecule through lsrK triggers different response pathways. These investigations demonstrated that lsrR, lsrK are indispensable for AI-2 uptake. These newly elucidated regulatory mechanisms and associations undoubtedly broaden the scope of the AI-2 quorum sensing system, and provide a solid foundation for further mathematical modeling of the dynamics and system behaviors in E. coli. Finally, a tight coupling of experimental manipulation with mathematical analysis, as demonstrated in this study, provides a good example for systematically investigating