Energy dependency on the salt-resistance of Staphylococcus aureus: Effects of various inhibitors on the growth in high salinity condition

It has previously been shown that the barrier system for high environmental salinity is closely related to the salt-resistance of Staphyloccus aureus. The present investigation was undertaken to clarify the energy dependency for the maintenance of intracellular univalent cation contents in cells grown on high concentration of salt containing medium. The results are summarized as follows: (1) The growth of 10% NaCl-Staph which was grown in the 10% NaCl containing nutrient broth was more sensitive to NaN3 than Normal-Staph which was grown only on nutrient broth. The anaerobic conditions in both media demonstrated a more powerful effect on growth inhibition of 10% NaCl-Staph than Normal-Staph. Therefore, 10% NaCl-Staph must have a higher energy dependency than Normal-Staph. (2) The high sensitivity to uncouplers, such as DNP and FCCP in 10% NaCl-Staph, also suggested an energy dependency which was probably related to respiration and not to anaerobic glycolysis. (3) The intracellular Na+ contents of Normal-Staph and 10% NaCl-Staph were 12.0 and 152.9 mmoles per Kg wet weight of cells respectively, and the content of K+ in 10% NaCl-Staph (90.2 mmoles per Kg wet weight) was lower than that of Normal-Staph (215.8 mmoles per Kg wet weight). These intracellular Na+ and K+ contents were strongly affected by the addition of various inhibitors to the medium. The measurements of intracellular univalent cation contents indicated the existance of an adaptively developed barrier system in 10% NaCl-Staph and the existence of energy-dependent transport mechanisms for efflux of Na+ in Normal-Staph and for the influx of K+ in 10% NaCl-Staph.