Magnesium requirement of Staphylococcus aureus for repair from sublethal heat injury

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Abstract
Heating in potassium phosphate buffer causes Staphylococcus aureus to lose its salt tolerance and 30–40% of its cellular Mg2+. Repair from injury (regain of salt tolerance) occurred when injured cells were incubated under optimal conditions in synthetic media containing penicillin to prevent growth. Cells died when phosphates or amino acids were omitted from the medium. Omission of vitamins, glucose, Na+, and K+ had no effect. Omission of Mg2+ diminished repair. In a minimal repair medium (MRM) which contained only 3 × 10−6 M Mg (as an impurity), injured cells rapidly regained their original Mg content. About 20–50% of the cells also regained their salt tolerance provided that less than 109 cells/ml were used. With 1010 cells/ml there was no repair and cellular Mg content was half that of the control. Addition of 10−3 M ethylenediaminetetraacetic acid (EDTA) to MRM also prevented repair. Addition of 10−2 M Mg to MRM + 10−3 M EDTA permitted complete repair.