This project is concerned with the effect of food structure on microbial growth. It has been established that food structure perturbs lag time, growth rate and the boundaries of the growth. The observed effects are commonly a reduction in growth rate, an extension of the lag time, and a shrinking of the habitat domain, although in some cases the colonial state results in faster growth. A common feature of these phenomena is the growth of the organisms in colonies, rather than as their plankton that. <P> The aim is to determine the mechanisms of these effects. Local stress conditions within colonies represent potential sites for bacterial adaptation by selective gene expression. The modification of the local environment within and around bacterial colonies will be predicted using cellular automaton computer tools, rate and stoichiometric constants derived from bioreactor technology and validation by fluorescence techniques. The effect of modification of the local environment on gene expression associated with stress response and virulence will be studied using reporter gene fusions.