Formation and conversion of oxygen metabolites by Lactococcus lactis subsp lactis ATCC 19435 under different growth conditions
Publikation/Tidskrift/Serie: APPLIED AND ENVIRONMENTAL MICROBIOLOGY
Förlag: AMER SOC MICROBIOLOGY
A semidefined medium based on Casamino Acids allowed Lactococcus lactis ATCC 19435 to grow in the presence of oxygen at a slow rate (0.015 h(-1)). Accumulation of H2O2 in the culture prevented a higher growth rate. Addition of asparagine to the medium increased the growth rate; whereby H2O2 accumulated only temporarily during the lag phase. H2O2 is an inhibitor for several glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase being the most sensitive. Strain ATCC 19435 contained NADH oxidase (maximum specific rate under aerobic conditions, 426 nmol of NADH min(-1) mg of protein(-1)), which reduced oxygen to water, whereby superoxide was formed as a by-product. H2O2 originated from the dismutation of superoxide by superoxide dismutase. Although H2O2, was rapidly destroyed under high metabolic fluxes, neither NADH peroxidase nor any other enzymatic H2O2-reducing activity was detected. However, pyruvate, the end product of glycolysis; reacted nonenzymatically and rapidly with H2O2 and hence was a potential alternative for scavenging of this oxygen metabolite intracellularly. Indeed, intracellular concentrations of up to 93 mM pyruvate were detected in aerobic cultures growing at high rates. It is hypothesized that self-generated pyruvate may serve to protect L. lactis strain ATCC 19435 from H2O2.
- Biology and Life Sciences
- ISSN: 0099-2240