Intellectual merit. The research is directed at determining the role of chemical communication among bacteria in biofilm formation. A small molecule known as autoinducer 2 (AI-2) is produced and secreted by diverse species of bacteria. High levels of AI-2 accumulate when cells exist at high density, as they do in the mixed-species aggregates known as biofilms. Biofilms frequently coat the surfaces of both natural and man-made surfaces, and cells living within them are protected from many chemical, physical, and biological agents that threaten free-living bacteria. We find that AI-2 is a potent chemoattractant for E. coli and have identified two proteins that serve as the receptor for AI-2. The project has two aims. (1) To determine the mechanism by which the AI-2 binding protein LsrB interacts with the transmembrane signal-transducer protein Tsr to initiate a chemotaxis response. (2) To determine whether AI-2 attracts free-swimming E. coli cells to biofilms and helps them to adapt themselves metabolically to biofilm life. Broader impacts. The research will be pursued in part by undergraduate and graduate students, who will receive training in molecular biology, bacterial physiology, and microfluidic nanotechnology. The research will be closely integrated with course work. The research is highly interdisciplinary. The investigators include a molecular microbiologist, a chemical engineer, a physical biochemist, and a synthetic organic chemist. This provides an excellent opportunity for training students. In addition, the research addresses an important environmental problem. Biofilms foul surfaces and serve as reservoirs for harmful bacteria in a variety of habitats. Knowledge about the chemical signals bacteria use to coordinate their activities to form and maintain unwanted biofilms can be applied to combat them.