Influence of magnesium and manganese on some biological and physical properties of tetracycline.

Accumulation of (3)H-tetracycline in nonproliferating cells of susceptible and resistant strains of Escherichia coli and Staphylococcus aureus in tris(hydroxymethyl)aminomethane (Tris) buffer (10 mm, pH 7.5) was significantly decreased in the presence of 5 to 40 mm MgCl(2) and increased in the presence of 5 to 10 mm MnCl(2). When the bacteria first accumulated (3)H-tetracycline in plain Tris.HCl, and the metal salts were thereafter added, a prompt decrease or increase in radioactivity of the cells was observed after the addition of Mg(2+) or Mn(2+), respectively. In phosphate buffer (10 mm, pH 7.5), the effect of Mg(2+) was delayed. Three minutes after addition of (3)H-tetracycline, uptake was as in the control cell suspension, but thereafter it dropped rapidly. When (3)H-tetracycline was incubated with Mg(2+) before addition to the bacterial suspension, uptake was scarcely measurable. The addition of Mg(2+) to growing cultures of S. aureus and E. coli caused a marked decrease in susceptibility; in contrast, no increase in susceptibility could be demonstrated when Mn(2+) was added. It was also demonstrated that Mg(2+) and Mn(2+) had distinct influences on the absorption spectrum, the optical rotatory dispersion, the circular dichroism, and the lipid solubility of tetracycline.