Investigation of the molecular basis of excitation and adaptation during chemotactic sensory transduction in bacteria

Bacteria lead stressful lives; they are constantly starving and contending with competitors. However, they have developed a sophisticated locomotion to escape harm and find favorable conditions. This is the process of chemotaxis. It arose billions of years ago, long before eukaryotes existed, and handles signaling tasks common to all cell sensory systems: detecting stimuli, processing and integrating inputs, and producing appropriate responses. Ease of genetic manipulation and cloning and rapid growth have proven important advantages for studying sensory processes in prokaryotes and general insights into cellular signaling mechanisms are emerging.

Bacteria pioneered the use of reversible protein phosphorylation to send an excitatory signal to alter motile behavior and the use of reversible receptor methylesterification to terminate the signal in the process of adaptation. The signal controls movement of the flagella. In our laboratory, we are studying how these receptors control protein phosphorylation and phosphoryl transfer in the gram positive bacterium Bacillus subtilis. They have been cloned and sequenced. Several proteins, in addition to the receptors, are also involved in this signal transduction process. We have cloned and manipulated the corresponding genes and are studying the interactions of the proteins. In addition there appear to be three adaptational systems at work to help extinguish the excitatory signal so that the bacteria are again poised to receive new information -- one involving the methyltransferase and methylesterase, another involving the novel proteins CheC and CheD in a feedback system with the response regulator CheY-P, and a third involving phosphorylation of CheV. This is a process that appears to be shared with the archaea, although not with Escherichia coli, where simple addition or hydrolysis of methyl groups on the receptors suffices for adaptation. Thus, it may be the means by which the primordial bacteria carried out chemotaxis. We are especially interested in characterizing three proteins -- CheC, CheD, and CheV -- which have no counterparts in E. coli, for they play important roles in this novel process. In general, having many of the genes cloned and selectively mutagenizing them has allowed us to get important insights into how the corresponding proteins are functioning.