Ferrous iron uptake by Bifidobacterium bifidum var. Pennsylvanicus: The effect of metals and metabolic inhibitors

Abstract

1. 1. Ferrous iron uptake studies in Bifidobacterium bifidum var. pennsylvanicus were carried out in a well-defined salt solution termed “modified Hanks solution” at both high iron concentrations (LAFIUS conditions) and low concentrations (HAFIUS conditions). 2. 2. Various divalent metals, Mn 2+, Zn 2+, Ni 2+ and Cu 2+, inhibited iron uptake under HAFIUS conditions in a non-competitive manner, and in pseudo-competitive manner under LAFIUS conditions. Cr 2+ had no effect. Co 2+ inhibited iron uptake competitively under HAFIUS conditions. 3. 3. Metabolic affectors that inhibited iron uptake both under HAFIUS and LAFIUS conditions were: tetraphenylphosphonium chloride, diethylstilbesterol, vanadate, carbonylcyanide- m-chlorophenylhydrazone, and a mixture of valinomycin and nigericin. Substances that stimulated iron uptake were KCl, valinomycin, and nigericin. 4. 4. Iron uptake under LAFIUS conditions in piperazine-buffered modified Hanks solution was higher than that in the acetate-buffered solution, and acetate inhibited iron uptake in the piperazine buffer. HAFIUS showed no difference. 5. 5. It is concluded that iron uptake in bifidobacteria is driven by an ATPase-dependent proton-motive force and that both the pH gradient and membrane potential are involved in this process. Mn 2+, Zn 2+, Ni 2+, and Cu 2+ may be transported via LAFIUS, but not HAFIUS. HAFIUS may transport only Co 2+ in addition to Fe 2+.