LACTOBACILLI, OXYGEN, METABOLISM AND ANTAGONISM

During the glucose oxidation by the homo- and hetero-fermentative Lact obacilli, the pyruvate which is formed is subsequently reduced by the lactate dehydrogenase (LDH) into lactate which accumulates in the cell . In some bacteria, the LDH is activated by fructose 1, 6 diphosphate (FDP). When the FDP is absent, the LDH activity is low and the glucose catabolism leads to terminal products such as acetate, acetoin or eth anol. In another Lactobacillus such as Lactobacillus plantarum, the LD H is FDP-independent but lactate is metabolized into acetate in the pr esence of oxygen and glucose depletion. The regulation of this process is unknown. Several enzymes may be involved in this process; the NAD- independent lactate dehydrogenase; the lactate oxidase; the pyruvate f ormate lyase, the pyruvate dehydrogenase; the pyruvate oxidase and the NADH oxidase with formation of H2O2 or H2O and also the NADH peroxida se. These activities were tested in L plantarum and L sake grown in si milar conditions. A pyruvate oxidase acitivity was detected only in L plantarum in aerobiosis. We have shown that the acetate produced from lactate inhibits the growth of pseudomonads in oxygenated co-cultures.