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The uptake of iron and the formation of penicillinase was examined in cultures of wild-typeStaphylococcus aureus . Uptake of iron was about twice as great atp H 4.7 as atp H 7.4 Atp H 4.7, increase in iron uptake in the range of 1.0 to 4.0 μg per mg of bacterial protein was associated with a progressive increase in the rate of penicillinase formation, but a direct correlation between cellular iron content and rate of enzyme formation was not demonstrated. Addition of iron to deferrated medium enhanced penicillinase formation atp H 6.5 to 7.4 two- to fourfold in cultures induced with benzylpenicillin and in uninduced cultures. To demonstrate an effect on the uninduced cells, it was necessary to increase iron uptake by preliminary incubation of cells with iron in buffer. Calcium and certain other ions depressed iron uptake at acidic and at neutralp H, and, presumably as a result of this action, depressed the formation of penicillinase. Iron did not enhance penicillinase formation atp H 4.7 by two penicillinase constitutive mutants nor by wild-type cells undergoing induction atp H 6.5 by cephalosporin C or methicillin. After removal of cephalosporin C or methicillin during an early phase of induction, residual synthesis of enzyme was increased by prior uptake of iron. The results are considered compatible with the concept that uptake of iron, especially at acidicp H, interferes with the formation or function of penicillinase repressor.

Relation Between Iron Uptake, p H of Growth Medium, and Penicillinase Formation in Staphylococcus aureus