Collaborative Research: Evolution of information processing in the Vibrio fischeri pheromone-signaling network

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Pheromone signaling controls many important bacterial behaviors, ranging from benign symbiotic relationships between bacteria and their hosts to colonization of human tissues and organs by bacterial pathogens. The aim of this project is to understand how the local environment (e.g., the environment in the host) affects pheromone signaling and bacterial behaviors such as colonization. This project combines molecular-based microbiology methods with physical and mathematical tools to develop a more complete experimental and theoretical picture of this process. The project will enhance education by training graduate and undergraduate students to perform cross-disciplinary laboratory research. These research experiences will prepare the students for a wide range of careers in the biosciences. The project also includes a formal training experience for secondary science teachers, primarily from high schools with large numbers of students from under-served populations. The most important elements of Vibrio fischeri pheromone signaling are the LuxI/LuxR signal-synthase/receptor, which produces and detects a 3OC6 homoserine lactone (HSL) pheromone, and the AinS/AinR synthase/receptor system, which employs a C8 HSL pheromone to drive a different signaling cascade. The complexity of these systems is enhanced by the crosstalk generated by LuxR's recognition of both HSL signals, by the fact that both Lux and Ain are modulated in response to the environment, and by the presence of positive feedback in both the Lux and Ain cascades. The primary goal of this project is to understand how the system gathers and integrates information from its environment. The specific aims are to (i) understand how the pivotal regulator LuxR and its variants integrate information from the two HSL signals, (ii) identify the activation states of the broader pheromone-signaling circuitry and explore how environmental inputs lead to specific outputs, and (iii) test the hypothesis that the architecture of this signaling system allows spatially-heterogeneous environments to trigger population-wide responses over extended distance and time scales. The project will use cytometry and gene reporter methods to characterize LuxR interactions and system states. It will also use microfluidics and microscopy to explore signaling dynamics in heterogeneous environments. The results are expected to yield new insights into how bacteria use environmental cues to control population-level behaviors.