Article| Volume 79, ISSUE 5, P758-766, May 1996

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Hydrogen Peroxide Production and Oxidation of Ferrous Iron by Lactobacillus delbrueckii ssp. bulgaricus

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      Hydrogen peroxide was produced by Lactobacillus delbrueckii ssp. bulgaricus ATCC 11842 only in the presence of glucose at pH 6.5 and 5.0 in the presence of air. Production of H2O2 was minimal following the heating of cells, in the presence of catalase, and at low partial pressure of O2. Production of H2O2 was lower at pH 5.0 than at pH 6.5; H2O2 was apparently produced by a cytosolic NADH oxidase. Lactobacillus delbrueckii ssp. bulgaricus was able to bind nanomolar quantities of iron when incubated in the presence of micromolar amounts of Fe2+. This binding was the result of oxidation of the Fe2+ by H2O2 produced and the subsequent surface binding of the resulting Fe(III), most likely in the form of Fe(OH)3. Ferric iron that was complexed with citrate or lactate was not bound. Little, if any, Fe2+ was internalized by the cells, and the particulate fraction of the microorganism lacked ferroxidase activity. The Fe(OH)3 associated with the cells was bound to specific binding regions of the cell surface that were sensitive to trypsin digestion and that could be protected against such digestion by binding endogenously or exogenously produced Fe(OH)3. The particulate fraction of L. delbrueckii ssp. bulgaricus was able to bind more Fe(OH)3 than comparable quantities of intact cells, the additional binding sites apparently originating from the cytosol side of the membranes. We concluded that L. delbrueckii ssp. bulgaricus was able to remove Fe2+ from its environment in the presence of air but not under anaerobic conditions. In this respect, this organism is less effective than bifidobacteria as a host defense factor in vivo.

      Key words

      Abbreviation key:

      pO2 (partial pressure of O2)


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