FERROUS IRON OXIDATION BY LACTOBACILLUS-ACIDOPHILUS AND ITS METABOLIC PRODUCTS

Lactobacillus acidophilus (ATCC 4356), grown in trypticase-phytone-yeast extract medium under anaerobic conditions, was capable of accumulating nanomolar quantities of iron when presented with Fe2+ at pH 6.5. A major factor in the ability of the organism to accumulate iron was its ability to produce and export H2O2, which oxidized Fe2+ to Fe(III). The latter was bound to the cell surface by a trypsin-sensitive protein. H2O2 production was inhibited by low p(O2) and glucose. L. acidophilus contained an Fe2+ transport mechanism and an intracellular heat-sensitive ferroxidase comparable to that of bifidobacteria. Lactate produced by the organism facilitated Fe2+ oxidation by O-2, but the Fe(III) produced remained sequestered by the lactate. It was concluded that L. acidophilus may participate in the nutritional immunity scheme under certain circumstances.