Abstract
Aerobic and respiratory cultivations provide benefits for some lactic acid bacteria (LAB). Growth, metabolites, enzymatic activities (lactate dehydrogenase; pyruvate and NADH oxidases, NADH peroxidase; catalase), antioxidant capability and stress tolerance of Lactobacillus casei N87 were evaluated in anaerobic, aerobic and respiratory (aerobiosis with heme and menaquinone supplementation) batch cultivations with different dissolved oxygen (DO) concentrations. The expression of pox (pyruvate oxidase) and cydABCD operon (cytochrome bd oxidase complex) was quantified by quantitative Real Time polymerase chain reaction. Respiration increased biomass production compared to anaerobiosis and unsupplemented aerobiosis, and altered the central metabolism rerouting pyruvate away from lactate accumulation. All enzymatic activities, except lactate dehydrogenase, were higher in respiratory cultures, while unsupplemented aerobiosis with 60% of DO promoted H2O2 and free radical accumulation. Respiration improved the survival to oxidative and freeze-drying stresses, while significant numbers of dead, damaged and viable but not cultivable cells were found in unsupplemented aerobic cultures (60% DO). Analysis of gene expression suggested that the activation of aerobic and respiratory pathways occurred during the exponential growth phase, and that O2 and hemin induced, respectively, the transcription of pox and cydABCD genes. Respiratory cultivation might be a natural strategy to improve functional and technological properties of L. casei.
Highlights
Lactic acid bacteria (LAB) are recognized as oxygen-tolerant anaerobes, usually lacking catalase and an active electron transport (ET) chain
We have evaluated the effect of anaerobic, aerobic (O2) and respiratory (O2, heme and menaquinone) growth, as well as of dissolved oxygen concentration (30% or 60% DO) on the biomass yield, metabolites, activities of O2-related enzymes, antioxidant capability and stress tolerance of respiration-competent strain L. casei N87
Growth at 60% of DO without supplementation significantly (Tukey’s HSD, p
Summary
Lactic acid bacteria (LAB) are recognized as oxygen-tolerant anaerobes, usually lacking catalase and an active electron transport (ET) chain. The aerobic (presence of O2, no cofactors) pathway for energy production involves pyruvate oxidase (POX) and acetate kinase (ACK) activities, which promote the oxidation of pyruvate into acetate with production of CO2, H2O2 and extra ATP. In most LAB species the activation of aerobic respiration requires exogenous supplementation of hemin or hemin and quinone (usually menaquinone). Using exogenous heme and menaquinone, a minimal respiratory chain, consisting of an electron donor (NADH dehydrogenase), a quinone electron shuttle (menaquinone) and a terminal O2 reductase (cytochrome bd oxidase) may be activated [3, 2]. In prokaryotes the membrane oxidase may promotes physiological functions (i.e. colonization of O2-poor environments by pathogenic and commensal bacteria, O2-scavenging activity, survival to stress; [4]) that may contribute to the robustness of bacterial cells. The implication of iron-sulphur (Fe-S) proteins in respiratory electron transfer and proton efflux has never been demonstrated in LAB
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