Growth inhibition of Escherichia coli by dichloromethane in cells expressing dichloromethane dehalogenase/glutathione S-transferase

Dichloromethane (DCM) dehalogenase converts DCM to formaldehyde via the for mation of glutathione metabolites and generates 2 mol HCI per mol DCM forma tion or glutathione metabolites and generates 2 mol HCI per mol DCM metabol ized. Growth of Escherichia coli expressing DCM dehalogenase was immediatel y and severely inhibited during conversion of 0.3 mM DCM. Intracellular pH (pH(i)) rapidly decreased and chloride ions were steadily released into the medium. Bacterial growth resumed after completion of DCM conversion and ce ll viability was unaffected. At 0.6 mM DCM there was no recovery from growt h inhibition in liquid culture due to the build-up of inhibitory concentrat ions of formaldehyde. DCM turnover stimulated potassium efflux from cells, which was suppressed by glucose. The potassium efflux, therefore, did not c ontribute to growth inhibition. It was concluded that initial growth inhibi tion results from lowering of the cytoplasmic pH. but severity of growth in hibition was greater than expected for the change in pH(i). Possible contri butors to growth inhibition are discussed.