Repression of Phenolic Acid-Synthesizing Enzymes and Its Relation to Iron Uptake in Bacillus subtilis

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RESUMO

Excretion of the metal-chelating phenolic acid, 2,3-dihydroxybenzoate, by a tryptophan-requiring strain (M-13) of Bacillus subtilis was inversely proportional to the iron added to the medium. Addition of iron as the ferric chelates of two secondary hydroxamates (ferri-schizokinen and Desferal) markedly reduced excretion. Synthesis of 2,3-dihydroxybenzoate from chorismate by extracts of B. subtilis M-13, grown in low-iron medium, was unaltered by additions of FeSO4, FeCl3, ferrischizokinen, 2,3-dihydroxybenzoate, the 2,3-dihydroxybenzoate-iron complex, or by extracts of cells grown in high-iron medium (which contained no demonstrable 2,3-dihydroxybenzoate-synthesizing activity) to the extracts of “low-iron cells.” Iron control seemed to involve repression of synthesis of the enzymes in the 2,3-dihydroxybenzoate pathway. Both ferri-schizokinen and 2,3-dihydroxybenzoate plus iron enhanced considerably the otherwise minimal repressive effects of iron at low concentrations. Ferri-schizokinen delayed derepression of the pathway in B. subtilis M-13, and reduced its rate of synthesis after derepression. Addition of FeSO4 to derepressed cells of B. subtilis M-13 halted synthesis of the enzymes after a lag period. The effect of the ferric hydroxamates was related to the capacity of B. subtilis M-13 to incorporate 59Fe3+ from Desferal-59Fe3+. Cellular accumulation of 59Fe3+ from Desferal-59Fe3+ after 20 min was nearly double that incorporated from 59FeCl3.

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