What regulatory processes govern whether a bacterium chooses to swim in liquid, to induce the specific swarmer cell program in order to move over and colonize surfaces, or to become less mobile and more adhesive in order to form biofilms? The marine bacterium Vibrio parahaemolyticus is an excellent model organism in which to address this question because the distinctions between the swimming, swarming, and sticky biofilm-proficient cells are very profound for this organism. Surface-associated growth promotes global, genome-wide reprogramming of gene expression resulting in an altered cell type and the induction of an entirely new motility system that is not expressed by the swimmer cell. This alternate system allows extremely rapid movement over surfaces, which is called swarming. Growth on surfaces can also result in robust biofilm formation. Gene sets have been identified that are reciprocally regulated in response to growth on surfaces; specifically motility and adhesive genes as well as the regulatory genes that govern the expression of these gene sets. These regulatory genes, named scr, encode potential signal transduction proteins containing GGDEF and EAL signature domains, which possess enzymatic activities causing synthesis and degradation of the signaling nucleotide c-di-GMP. This project focuses on the role of c-di-GMP in programming gene expression and behavior. It is hypothesized that a specific array of Scr signal transducing proteins, capable of detecting and integrating diverse environmental signals by modulating the level of c-di-GMP, influences the decision to swarm or stick. A low concentration of c-di-GMP favors surface mobility; whereas high levels of this nucleotide promote a more adhesive and sessile, or biofilm-proficient, cell type. This project focuses on: 1, defining the scope of the scr c-di-GMP network by using genetic screens to detect potential scr sensors and fluorescent fusion proteins to determine protein localization; and 2, establishing the molecular basis of c-di-GMP control of gene expression by examining candidate transcriptional regulators of swarming and sticking. Thus, this research is designed to map a complex regulatory circuit controlling processes by which bacteria sense, integrate, and respond to multiple signals in their environment, and will provide insight into how bacteria make decisions.
Broader Impact These studies will reveal general principles with respect to the developmental program that enables bacteria to successfully colonize surfaces, as well as indicate the specific surface-adaptation strategies utilized by V. parahaemolyticus. This project is specifically designed to integrate teaching and research by implementing an undergraduate-driven discovery project to examine environmental signal input and define new output targets. This discovery plan will allow the direct participation of undergraduate students in the research process. Students will learn to make observations, formulate hypotheses and test their ideas; they will also develop their writing and public speaking skills. Importantly, the student projects are formulated in such a manner that the students will also gain knowledge of the broad arsenal of genetic, physiological, molecular biological, and bioinformatics-based techniques that can be applied to unravel programs of gene control and the underlying basis for bacterial behavior.
