ABSTRACT
Most living organisms, including bacteria, require iron for growth. Bifidobacteria are not an exception to this rule: they require ferrous iron for growth, and such growth may be inhibited by ferrous iron chelators and divalent metal ions. The transport of iron in bifidobacteria is dependent on the generation of the proton gradient, and it is likely that the resulting membrane potential is the most important force that delivers iron to the cell interior. The transport of nutrients is generally studied in nongrowing cells. Bifidobacteria, being strict anaerobes, will not grow even if the uptake studies are carried out over a period of several hours in air. Iron transport in microorganisms has largely been studied in connection with the ferric iron transporters called siderophores. Ferric iron is by far the more abundant iron source for microorganisms, and all aerobic and facultative anaerobic organisms have developed ways and means of bringing such iron into the cell.
