Regulation of staphylococcal toxic shock syndrome toxin-1 and total exoprotein production by magnesium ion

Abstract

The effect of Mg2+ on in vitro production of extracellular proteins and, specifically, of toxic shock syndrome toxin-1 (TSST-1), by Staphylococcus aureus in a chemically defined medium was examined. As previously observed, the organisms did not proliferate in the absence of divalent cations. Low levels of Mg2+ (0.02 to 0.04 mM) permitted submaximal proliferation and elevated production of exoproteins. When the Mg2+ concentration was raised to 0.4 mM, multiplication was optimal and exoprotein levels were depressed. Ca2+ and Mn2+ diminished the effect of limiting Mg2+. The increased levels of exoproteins were not due to cell lysis or leakage since intracellular TSST-1 levels were not high enough to account for the increase in extracellular TSST-1 and since the intracellular enzyme, lactate dehydrogenase, was not found in culture supernatants. Cells cultured in low levels of Mg2+ remained in logarithmic growth longer than did those cultured in high concentrations of Mg2+ and, unlike the latter, produced exoproteins throughout the logarithmic growth phase. Low Mg2+ had no effect on cultures in the stationary phase, and organisms cultured in low Mg2+ recovered fully when transferred to high Mg2+. We conclude that, when cultured in medium deficient in Mg2+, S. aureus responds early in the growth cycle by increasing production of many extracellular proteins, including TSST-1.