Influence of Magnesium and Manganese on Some Biological and Physical Properties of Tetracycline

Accumulation of3 H-tetracycline in nonproliferating cells of susceptible and resistant strains ofEscherichia coli andStaphylococcus aureus in tris(hydroxymethyl)aminomethane (Tris) buffer (10 mm ,p H 7.5) was significantly decreased in the presence of 5 to 40 mm MgCl2 and increased in the presence of 5 to 10 mm MnCl2 . When the bacteria first accumulated3 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 Mg2+ or Mn2+ , respectively. In phosphate buffer (10 mm ,p H 7.5), the effect of Mg2+ was delayed. Three minutes after addition of3 H-tetracycline, uptake was as in the control cell suspension, but thereafter it dropped rapidly. When3 H-tetracycline was incubated with Mg2+ before addition to the bacterial suspension, uptake was scarcely measurable. The addition of Mg2+ to growing cultures ofS. aureus andE. coli caused a marked decrease in susceptibility; in contrast, no increase in susceptibility could be demonstrated when Mn2+ was added. It was also demonstrated that Mg2+ and Mn2+ had distinct influences on the absorption spectrum, the optical rotatory dispersion, the circular dichroism, and the lipid solubility of tetracycline.