Effects of Mg 2+ and Ca 2+ on Fe 2+ uptake by Bifidobacterium thermophilum

Abstract

Ferrous iron uptake was investigated in Bifidobacterium thermophilum (B. thermophilum) in the presence of Mg 2+ and Ca 2+ with the following findings: 1. 1. Mg 2+ inhibited Fe 2+ accumulation in the cells in a dose-dependent manner at 37°, but not at 0°. Removal of Mg 2+ from the medium resulted in a resumption of rapid iron uptake. 2. 2. Mg 2+ had no effect on the binding of Fe 2+ by B. thermophilum protoplasts, its cellular particulate fraction, or distribution between the particulate and soluble fractions. 3. 3. Ca 2+ exerted a stimulatory effect on iron uptake by B. thermophilum, but was not able to reverse the inhibitory effects of Mg 2+. 4. 4. It was concluded that Mg 2+ has no effect on the binding of iron on the surface or interior of B. thermophilum and that it affected the Fe 2+ transport mechanism (permease) in a reversible manner. It is possible that iron and magnesium share the same permease in this microorganism.