EFFECTS OF EXTRACELLULAR PH ON THE INTRACELLULAR PH, MEMBRANE-POTENTIAL, AND GROWTH-YIELD OF MEGASPHAERA-ELSDENII IN RELATION TO THE INFLUENCE OF MONENSIN, ETHANOL, AND ACETATE

Megasphaera elsdenii was able to grow when the extracellular pH (pH(e)) was as low as 5.5, and maintained a near-neutral intracellular pH (pH(i)) in the wide range of pH(e). The membrane potential (DELTA-phi) and Y(glucose) were decreased as the pH(e) was lowered from 6.7 to 5.5. When M. elsdenii was grown in the presence of 10 mg/l monensin, 3% ethanol, or 25 mM acetate, both Y(glucose) and pH(i) were decreased as the pH(e) declined. Acetate alleviated the growth inhibition by ethanol at low pH(e). Unexpectedly, DELTA-phi was increased remarkably by monensin or acetate only at pH(e) 6.0; this is inexplicable at present. Ethanol decreased the DELTA-phi as the pH(e) was decreased.