Bacterial chemotaxis: biochemistry of behavior in a single cell.

Bacterial chemotaxis is a primitive behavioral system that shows great promise for being amenable to a description of its molecular mechanism. In Gram-negatives like Escherichia coli, addition of amino acid attractant begins a series of events, starting with binding to certain intrinsic membrane proteins, the MCPs, and ending with a period of smooth swimming. Immediately, methyl-esterification of these MCPs begins and continues during this period. By contrast in the Gram-positive Bacillus subtilis, demethylation of MCPs occurs during the same period. At least two other mechanisms for mediating chemotaxis toward the attractants oxygen and phosphotransferase sugars exist in E. coli, and in these, changes in methylation of MCPs plays no role. Moreover, chemotaxis away from many repellents by B. subtilis appears to involve different mechanisms. Many of the repellents include drugs and toxicants, many of them man-made, so that chemoreceptors could not have specifically evolved; yet the bacteria are often exquisitely sensitive to them. Indeed, the B. subtilis membrane seems to act like a generalized antenna for noxious membrane-active substances.