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 aerobic/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 obtained. For anaerobic respiration with nitrate, fumarate or Me2SO Delta p decreased only slightly by about 20 mV in contrast to earlier assumptions, whereas Delta p dropped by approximately 40 mV during fermentation. Under all conditions, the membrane potential (Delta Psi) contributed the major portion to Delta p. The cellular ATP levels were highest 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 constant due to equivalent changes of the ADP contents. Transition to the stationary growth phase caused a massive drop in the ATP content. It is concluded that, during anaerobic respiration, the energetic situation for the bacteria is very similar to that for aerobic growth with respect to Delta G'(Phos) and Delta p whereas, for fermentation, a significant decrease in Delta p was observed. The consequences for the cellular energetics and for the regulation of the aerobic/anaerobic transition are discussed.