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J Bacteriol. 1972 May; 110(2): 468-476
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

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

Rapaport Laboratories for Microbiology, Bar-Ilan University, Ramat Gan
Department of Microbiology, Asaf Harofe Government Hospital, Tel-Aviv University Medical School, Zrifin, Israel

ABSTRACT

Accumulation of ³H-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 MgCl₂ and increased in the presence of 5 to 10 mM MnCl₂. When the bacteria first accumulated ³H-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, pH 7.5), the effect of Mg²⁺ was delayed. Three minutes after addition of ³H-tetracycline, uptake was as in the control cell suspension, but thereafter it dropped rapidly. When ³H-tetracycline was incubated with Mg²⁺ before addition to the bacterial suspension, uptake was scarcely measurable. The addition of Mg²⁺ 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 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.