Harwood 9316257 Aromatic compounds are abundant in the environment as major components of plant material (lignin) and as toxic by-products of industrial activities. Although we know something about how these compounds are degraded, not much is understood about how bacteria detect them in the environment. Several genera of motile bacteria, including Pseudomonas, have a strong attraction to aromatic acids. We will study the molecular basis for chemotaxis to 4- hydroxybenzoate and related aromatic acids in P. putida. Recently, a gene encoding an apparent chemoreceptor for these compounds was cloned and sequenced. The aromatic acid receptor is a membrane protein with a structure different from other bacterial chemoreceptors that have been described. We will attempt to define the chemosensory signaling domain of the aromatic acid chemoreceptor by metagenesis, and then asses a possible role for methylation and/or phosphorylation of the protein in chemosensory signal transduction/adaptation. The genetic organization of the region contiguous to the chemoreceptor gene will be determined, and the regulatory requirements for chemoreceptor gene expression will be defined. Finally, genes that are required for P. putida chemotaxis will be cloned and sequenced as a means of putting the aromatic acid chemoreceptor "in context" with the central chemotaxis machinery of this bacterium. Since the chemoreceptor protein for aromatic acids appears to have distinctive structural characteristics, our studies will broaden current concepts about mechanisms of bacterial chemoreception and sensory transduction. %%% Many environmental pollutants have a benzene ring as the main structural constituent and are classified as aromatic compounds. Bacteria have the ability to remove aromatic compounds from nature, and there is great interest in harnessing this ability to develop new methods for bioremediation to use in toxic waste management. To effectively use bioremediation, we need to understand how bacteria degrade aromatic compounds, and we also need to know how bacteria sense the compounds in nature in the first place. This project will examine the behavioral responses (chemotaxis) of bacteria to aromatic compounds. The bacteria we study are motile and can detect these compounds as food in their surroundings. Our main experimental plan will be to develop mutants that don't sense the compounds and then determine what is missing in the cell that is responsible. Once identified, we will clone and analyze the gene(s). If we can understand the mechanism(s) responsible for attraction to aromatic compounds (which involves one or more receptors), then it may be possible to devise strategies to recruit bacteria to bioremediation sites. ***
