The effect of pH on the growth and metabolism of Streptococcus bovis in continuous culture

Streptococcus bovis H13/1 was grown anaerobically at pHs between 5.0 and 6.5 in a glucose-limited chemostat at a dilution rate of 0.05/h. The growth yield and the production of acetate, ethanol and formate decreased at pHs less than 6.5 whereas the production of lactate increased at the lower pH values. When a culture was subjected to sequential pH changes, growth yield and fermentation products were influenced not only by the pH existing in the culture medium but also by the metabolic activity of the cells at the preceding pHs in the sequence. The results are discussed in relation to the mechanisms available for the maintenance of pH homeo-stasis and for the metabolic control of fermentation pathways in Strep. bovis.