Sensory adaptation in bacterial chemotaxis: regulation of demethylation

The behavioral responses of chemotactic bacteria to environmental stimuli are initiated by a family of membrane-bound transducer proteins that communicate excitatory signals to the flagellar apparatus. The adaptation process appears to turn off the excitatory signal and is mediated by the reversible methylation of multiple sites on the transducer proteins. The activities of two chemotaxis-specific enzymes, a methyltransferase and a methylesterase, are regulated during adaptation to maintain behavioral responsiveness. To monitor stimulus-induced changes in methylesterase activity in intact cells, we quantitated the continuous generation of methanol, the end product of the demethylation reaction, in a flow device. In this paper we describe studies of the regulation of the demethylation process. Changes in methylesterase activity after the simultaneous addition of opposing stimuli through two different transducer classes suggest that the sensory information detected by these transducers was integrated and that this integrated signal controlled demethylation.