SENSORY TRANSDUCTION IN BACTERIA

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Most pathways for bacterial chemotaxis involve methylation of the sensory transducer. Studies in this laboratory are concerned with methylation-independent pathways in Salmonella typhimurium and Escherichia coli for chemotaxis to oxygen (aerotaxis) and to sugars transported by the phosphotransferase system (PTS). The methylation-independent and the methylation-dependent pathways converge before the switch that controls the direction of rotation of the flagellar motors. The interaction between these pathways and also the point of convergence will be investigated. The mechanism by which transducer methylation is depressed by substrates of the PTS, and the role of cGMP in this phenomenon will be studied using behavior, in vitro assays of transducer methylation and demethylation, and protein chemistry. It is proposed to determine the mechanism by which deletion of protein methylesterase (CheB) inverts the aerotactic response. Chemotaxis to PTS sugars is unique in requiring an intact transport system for the attractant. It is proposed to identify the components necessary for sensory transduction, their function, and particularly the mechanism of adaption. Initial investigations will be concerned with the phosphorylatio of PTS components at sites other than the active site. Aerotaxis is mediated by a "protometer" that detects changes in the proton motive force and transmits a signal that results in appropriate behavioral change. As a first step toward the long range goal of identifying and characterizing the components of the aerotactic system, E. coli mutants in aerotaxis wilal be selected, mapped and characterized. The mechanism of the repellent response to high concentrations of oxygen will be investigated. ATP is required for either signal transmission or the flagella switch. 8-Azidoadenosine added to the cells can substitute for adenine in activating chemotaxis. After confirming the formation of azidoadenosine triphosphate, the cells will be irradiated and fractionated to identify ATP-binding components of the chemotactic pathway. Subsequently, the mode of action of ATP in chemotaxis will be determined.