Lactic acid bacteria hydrogen peroxide

Catalases catalyze the conversion of hydrogen peroxide to dioxygen and water. Two families of catalases are known, one having a heme cofactor and the second a structurally distinct family, found in thermophilic and lactic acid bacteria. The manganese enzymes contain a binuclear active site and the functional form of the enzyme cycles between the (Mn )2 and the (Mn )2 oxidation states. When isolated, the enzyme is in a mixture of oxidation states including the Mn /Mn superoxidized state and this form of the enzyme has been extensively studied using XAS, UV-visible, EPR, and ESEEM spectroscopies. Multifrequency EPR and microwave polarization studies of the (Mn )2 catalytically active enzyme from L. plantarum have also been reported. ... 

The mechanism(s) by which lactic acid bacteria inhibit or inactivate other bacteria is not totally clear. Daly et al. (1972), Speck (1972), and Gilliland and Speck (1972) have cited evidence which suggests that the following may be involved (1) production of antibiotics such as nisin, diplococcin, acidophilin, lactocidin, lactolin, and perhaps others (2) production of hydrogen peroxide by some lactic acid bacteria (3) depletion of nutrients by lactic acid bacteria, which makes growth of pathogens difficult or impossible (4) production of volatile acids (5) production of acid and reduction in pH (6) production of D-leucine and (7) lowering the oxidation-reduction potential of the substrate. 

Whittenbury, R. 1964. Hydrogen peroxide formation and catalase activity in the lactic acid bacteria. J. Gen. Microbiol. 35, 13-26. 

Lactic acid bacteria and bifidobacteria are preferred as protective and probiotic cultures, and have been used since the beginning of history as starter cultures. They have a long history of being safely used and consumed. LAB are widely used for fermentation of milk, meat, and vegetable foods. In fermentation of dairy products, lactose is metabolized to lactic acid. Other metabolic products, hydrogen peroxide, diacetyl, and bacteriocins may also play inhibitory roles and contribute to improving the organoleptic attributes of these foods, as well as their preservation (Messens and De Vuyst, 2002). 

Hydrogen peroxide is generated by the lactic acid bacteria in the presence of oxygen. Hydrogen peroxide is bactericidal but is mainly important as one of the components of the lactoperoxidase system (Lindgren and Dobrogosz, 1990). 

Old yellow enzyme has been isolated only from yeast a similar enzyme, however, has been shown to account for the oxygen uptake of anaerobic lactic acid bacteria, which contain no demonstrable hemochromogens. The hydrogen peroxide produced in such respiration kills the organism. 

Inorganic compounds exhibiting antimicrobial activity also include hydrogen peroxide, phosphates or carbon dioxide, which is effective against fungi and gram-negative psychrotropic bacteria, but lactic acid bacteria and anaerobes are less inhibited. 

Some lactic acid bacteria reduce oxygen from the environment by forming hydrogen peroxide according to the following reaction ... 

The succession of bacterial species during alcoholic fermentation can be explained by a difference in the sensitivity of bacteria to interactions with yeasts. Interactions between lactic acid bacteria must also exist, simultaneously. Like other microorganisms, they can synthesize and liberate substances with antimicrobial activities. This problem has been examined closely in the milk industry, where the consequences are more serious. These substances are simple (hydrogen peroxide, organic acids, etc.) or more complex. Bacteriocins are a class of proteins whose bactericidal activity generally has a narrow range of action. It is sometimes even limited to the same species as the producing strain. Fundamental and applied research on... 

Bactericidal activity Lactobacilli ferment lactose to lactic acid, thereby reducing the pH to a level that harmful bacteria cannot tolerate. Hydrogen peroxide is also produced, which inhibits the growth of Gram-negative bacteria, ft has also been reported that lactic acid producing bacteria of the Streptococcus and Lactobacillus species produce antibiotics. 

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