Oxygen taxis and proton motive force in Salmonella typhimurium

The aerotactic response of Salmonella typhimurium SL3730 has been quantitatively correlated with a change in the proton motive force (delta p) as measured by a flow-dialysis technique. At pH 7.5, the membrane potential (delta psi) in S. typhimurium changed from -162 +/- 13 to -111 +/- 15 mV when cells grown aerobically were made anaerobic, and it returned to the original value when the cells were returned to aerobiosis. The delta pH across the membrane was zero. At pH 5.5, delta psi was -70 mV in aerobiosis and -20 mV in anaerobiosis, and delta pH was -118 and -56 mV for aerobic and anaerobic cells, respectively. A decrease in delta p resulted in increased tumbling, and an increase in delta p resulted in a smooth swimming response at either pH. Inhibition of aerotaxis at pH 7.5 by various concentrations of KCN correlated with a decreased delta p, due to a decreased delta psi in aerobiosis and little change in delta psi in anaerobiosis. At concentrations up to 100 mM, 2,4-dinitrophenol decreased delta psi, but did not inhibit aerotaxis because the difference between delta psi in aerobic and anaerobic cells remained constant. Considered as a whole, the results indicate that aerotaxis in S. typhimurium is mediated by delta p.