NOTES Staphylococcus aureus Osmoregulation: RolesforCholine, Glycine Betaine, Proline, andTaurine

Choline, glycine betaine, andL-proline enhanced thegrowthofStaphylococcus aureus athighosmolarity (i.e., theyacted asosmoprotectants) on various liquid andsolid defined media, while an osmoprotective effect oftaurine was shownonlyforcells growing on high-NaCl solid mediumthatlacked other osmoprotectants. Potassium poollevels were high, andthere was little difference inlevels incells grown atdifferent osmolarities. Glycine betaine accumulated tohighlevels inosmotically stressed cells, andcholine was converted toglycine betaine. Proline andtaurine alsoaccumulated inresponsetoosmotic stress buttolowerlevels thanglycine betaine. Staphylococcus aureus isamong themostosmotolerant of thenonhalophilic eubacteria, growing atwateractivities as lowas0.86(equivalent to3.5M NaCI)(35). Although much early workon osmoregulation concerned S.aureus (5,26), very little isknownabouttheunderlying mechanisms. Osmoregulation inthis organism isinherently interesting for several reasons.Unlike many other organisms which grow in environments ofelevated osmolarity, S.aureus alsogrows wellatlowosmolarities, suggesting an efficient means of regulating cytoplasmic osmolarity. S.aureus isalsoproba