ACCUMULATION OF IRON IN LACTIC-ACID BACTERIA AND BIFIDOBACTERIA

Lactobacillus acidophilus, L. delbrueckii var. bulgaricus, L. plantarum and Streptococcus thermophilum, all used extensively in the food industry, were tested for their ability to internalize and/or oxidize ferrous iron (Fe2+). For comparison some experiments were performed with bifidobacteria, B. thermophilum and B. breve. All organisms except L. bulgaricus could transport Fe2+ into the cell, where it was partially oxidized to the ferric form (Fe(III)). In addition, L. acidophilus and L. bulgaricus could oxidize Fe2+ to Fe(III) extracellularly through the elaboration of H2O2 into the medium when the experiments were carried out in air. L. bulgaricus elaborated H2O2 only in the presence of glucose, whereas L. acidophilus released H2O2 in absence of glucose. We concluded that lactic acid bacteria, like bifidobacteria, can exert some beneficial effects in animal organisms, or in food processing and storage, by making Fe2+ unavailable to harmful microorganisms.