The influence of the external pH on the production of modified protein A by Staphylococcus aureus

Abstract

External pH (pH 0) influences bacterial cell function primarily through the transmembrane proton motive force and the intracellular pH. These cell properties were measured during batch aerobic cultivations at different controlled pH 0 values of recombinant Staphylococcus aureus which expresses and exports to the medium a plasmid-encoded modified form of protein A. Proton motive force values at lower pH 0 were approximately the same as at pH 0 7.0, but decreased external pH reduced intracellular pH somewhat. Intracellular pH was similar at external pH values of 7.0 and 7.5. Significantly reduced proton motive force was observed at pH 0 7.5 relative to lower pH 0 values. Over the pH 0 range from 6.0 to 7.5 which was investigated, maximum protein A specific productivity was observed at pH 0 7.0. The results suggest that decreased productivity of extracellular protein A at low external pH results primarily from changes in intracellular metabolism while productivity decline at pH 0 7.5 is likely to be a consequence of altered cell membrane transport.