Christopher V. Rao, Department of Chemical Engineering, University of Illinois, 600 South Matthews Ave., 211 Roger Adams Laboratory, Box C-3, Urbana, IL 61801 and Supreet Saini, Chemical and Biomolecular Engineering, University of Illinois, 600 South Matthews Ave., 211 Roger Adams Laboratory, Box C-3, Urbana, IL 61801.
Salmonella typhimurium causes a variety of diseases ranging from mild gastroenteritis to life threatening systemic infections. During the course of infection, Salmonella invades intestinal epithelial cells using a type III secretion system (TTSS) encoded on Salmonella pathogenicity island 1 (SPI1). The SPI1 TTSS forms a needle-like structure that injects proteins directly into the cytosol of the host cells. These injected proteins commandeer the host cell's intracellular machinery to promote bacterial internalization.
Through the combined use of experimental and mathematical analysis, we demonstrate that coupled negative and positive feedback loops are involved in the regulation of the SPI1 TTSS. These interlocking loops form a bistable switch with an environmentally-tuned activation threshold.