Accumulation of tetracyclines by Escherichia coli K-12

Summary The passage of tetracycline and its derivative minocycline across the outer and cytoplasmic membranes of E. coli K-12 was investigated. A deep rough lipopolysaccharide core mutant was more sensitive to minocycline than wild-type bacteria. However, the sensitivity to tetracycline was only slightly altered. These data imply that hydrophobic and hydrophilic tetracyclines cross the outer membrane by different routes. Tetracycline chelates magnesium and may therefore cross the cytoplasmic membrane via the system normally involved in the active transport of magnesium. Mutants altered in their ability to transport magnesium were as sensitive to tetracycline as wild-type bacteria and the rate of uptake of labelled tetracycline by a mutant totally deficient in energy dependent magnesium accumulation was similar to that of the wild-type parental strain. Magnesium ions dispersed across the membrane are probably responsible for the binding of tetracycline to the cytoplasmic membrane.