Ferrous iron uptake by Bifidobacterium bifidum var. pennsylvanicus: the effect of metals and metabolic inhibitors

Abstract

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). Various divalent metals, Mn2+, Zn2+, Ni2+ and Cu2+, inhibited iron uptake under HAFIUS conditions in a non-competitive manner, and in a pseudo-competitive manner under LAFIUS conditions. Cr2+ had no effect. Co2+ inhibited iron uptake competitively under HAFIUS conditions. Metabolic affectors that inhibited iron uptake both under HAFIUS and LAFIUS conditions were: tetraphenylphosphonium chloride, diethylstilbesterol, vanadate, carbonylcyanide-m-chlorophenyl-hydrazone, and a mixture of valinomycin and nigericin. Substances that stimulated iron uptake were KCl, valinomycin, and nigericin. 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. 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. Mn2+, Zn2+, Ni2+, and Cu2+ may be transported via LAFIUS, but not HAFIUS. HAFIUS may transport only Co2+ in addition to Fe2+.