Transport of ferrous iron and lactate production in Bifidobacterium bifidum var. pennsylvanicus.

Initial rates of ferrous iron transport into Bifidobacterium bifidum var. pennsylvanicus were measured at low and high iron concentrations. The low affinity system (LAFIUS) had an apparent Km of 167 microM, the high affinity system (HAFIUS) had a Km of 50 microM. Iron removal from preloaded bifidobacteria revealed the existence of a labile and an inert iron pool in the bacterial cells. Iron uptake by the bifidobacteria was associated with lactate production, though lactate production could continue without iron uptake. Cessation of iron uptake and lactate production was not because of an exhaustion of any nutrient nor the accumulation of fermentation end products in the medium. It was apparently the result of an inactivation of the cellular enzyme machinery without replacing it through normal biosynthetic processes.