The overall goal of the proposed research is an understanding of the operation of a specific system of sensory reception and behavior, namely bacterial chemotaxis. The system, although rudimentary by comparison with behavior in higher organisms, is nonetheless quite complex. Study of the system contributes to an understanding of general principles of receptor function and organization, integration of sensory information, biological switching, and energy transduction. It also provides a foundation of basic knowledge regarding bacterial motility and behavior that can be of use in applied areas, such as medical microbiology, agricultural microbiology, and mechanisms of biodegradation. Within the overall goal, effort in the next few years will be focussed specifically on the composition, structure, and function of the effector organelle--the bacterial flagellar motor--including its switching elements. The primary organisms under study will be Salmonella typhimurium and Escherichia coli.