PHOSPHORYLATION-INDEPENDENT BACTERIAL CHEMORESPONSES CORRELATE WITH CHANGES IN THE CYTOPLASMIC LEVEL OF FUMARATE

Bacterial chemotaxis is based on modulation of the probability to swit ch the direction of flagellar rotation, Responses to many stimuli are transduced by a two-component system via reversible phosphorylation of CheY, a small cytoplasmic protein that directly interacts with the sw itch complex at the flagellar motor, We found that the chemorepellents indole and benzoate induce motor switching in Escherichia coli cells with a disabled phosphorylation cascade, This phosphorylation-independ ent chemoresponse is explained by reversible inhibition of fumarase by indole or benzoate which leads to an increased level of cellular fuma rate, a compound involved in motor switching for bacteria and archaea. Genetic deletion of fumarase increased the intracellular concentratio n of fumarate and enhanced the switching frequency of the flagellar mo tors irrespective of the presence or absence of the phosphorylation ca scade, These correlations provide evidence for fumarate-dependent meta bolic signal transduction in bacterial chemosensing.