The authors examined the intracellular solute composition of five strains of Staphylococcus aureus after growth in a medium of low water activity. Organic solutes within cell extracts were analyzed using an amino acid analyzer and nuclear magnetic resonance spectroscopy. Intracellular potassium content was assayed using a potassium-specific electrode. The results showed that the five S. aureus strains accumulated proline and glycine betaine intracellularly under these growth conditions. The levels of accumulated proline and glycine betaine were strikingly similar among the strains, despite differences in salt tolerance. During the course of these experiments it was also found that S. aureus strain RN4220 (a strain commonly used in genetic studies) was selectively impaired in its ability to utilize proline during osmoadaptation at 41°C.
Keywords: Water activity; compatible solute; osmoadaptation; osmoregulation.