Abstract
To elucidate the salt tolerance mechanism of Staphylococcus aureus, the adaptive changes of the contents of amino acids and water in the cell were studied by altering the salt concen-tration of the growth media.
Only a trace amount of proline was detected in the cells of S. aureus grown in a medium containing 0.1M NaCl. The cells grown in a medium containing 1.0 and 1.8M NaCl had 428 and 1, 440μmoles proline accumulated, respectively, per g of dry weight of cells. The intracellular water content was 1.70g/g dry wt. when cells were grown in a medium containing 0.1M NaCl. When the cells were transferred to a medium containing 1.8M NaCl, their water content decreased to 0.80g/g dry wt. within one minute, while their intracellular free proline content increased gradually from O to 1, 400μmoles/g dry wt. after incubation at 37C for 30 minutes. Meanwhile their water content increased to 0.88g/g dry wt. The accumulation of proline was found to be due to a temperature-dependent selective uptake from the medium. The accumulated proline was released quickly when the cells were transferred from a high salt medium to a low salt solution. The efflux of proline occurred at 0-4C, suggesting that the process might not be energy-dependent.
The role of proline and water content in the osmoregulation mechanism of S. aureus was made clear. The salt-tolerance mechanism was discussed, taking its correlation with adaptive changes in the cell-membrane constituents into consideration.
