Synthesis of Pyruvate Dehydrogenase in Staphylococcus aureus Is Stimulated by Osmotic Stress

The pyruvate dehydrogenase multienzyme complex (PDHC) was found to be upregulated by osmotic stress in the osmotolerant pathogen Staphylococcus aureus. Upregulation was detectable in the levels of both activity and protein and was judged to be about fourfold when sodium chloride was used to adjust the water activity (a(w)) of the growth medium to 0.94. The upregulation of the PDHC was also found to be humectant dependent and was greatest when impermeant, nonmetabolizable humectants were used to adjust a(w). Further experiments provided evidence that in addition to osmotic upregulation, the PDHC complex is also subject to catabolite repression, thus providing a possible explanation for the observation that high concentrations of carbohydrates are generally more inhibitory to the growth of this bacterial pathogen than are high concentrations of salts.