CHANGES IN THE PROTON POTENTIAL AND THE CELLULAR ENERGETICS OF ESCHERICHIA-COLI DURING GROWTH BY AEROBIC AND ANAEROBIC RESPIRATION OR BY FERMENTATION

The energetic parameters of Escherichia coli were analyzed for the aer obic/anaerobic transition. The electrochemical proton potential (Delta p) across the cytoplasmic membrane was determined in the steady state of respiration with O-2, nitrate, fumarate, dimethylsulfoxide (Me2SO) , and for fermentation. With O-2, a proton potential of -160 mV was ob tained. For anaerobic respiration with nitrate, fumarate or Me2SO Delt a p decreased only slightly by about 20 mV in contrast to earlier assu mptions, whereas Delta p dropped by approximately 40 mV during ferment ation. Under all conditions, the membrane potential (Delta Psi) contri buted the major portion to Delta p. The cellular ATP levels were highe st for aerobic growth (about 13 mu mol/g dry cells) and decreased to 3 -6 mu mol/g in anaerobic metabolism. Delta G'(Phos), however, was cons tant due to equivalent changes of the ADP contents. Transition to the stationary growth phase caused a massive drop in the ATP content. It i s concluded that, during anaerobic respiration, the energetic situatio n for the bacteria is very similar to that for aerobic growth with res pect to Delta G'(Phos) and Delta p whereas, for fermentation, a signif icant decrease in Delta p was observed. The consequences for the cellu lar energetics and for the regulation of the aerobic/anaerobic transit ion are discussed.