OXYGEN EFFECT ON BATCH CULTURES OF LEUCONOSTOC-MESENTEROIDES - RELATIONSHIP BETWEEN OXYGEN-UPTAKE, GROWTH AND END-PRODUCTS

Growth and lactose metabolism of a Leuconostoc mesenteroides strain we re studied in batch cultures at pH 6.5 and 30 degrees C in 101 modifie d MRS medium sparged with different gases: nitrogen, air and pure oxyg en. In all cases, growth occurred, but in aerobiosis there was oxygen consumption, leading to an improvement of growth yield Y-X/S and speci fic growth rate compared to anaerobiosis. Whatever the extent of aerob ic growth, oxygen uptake and biomass production increased with the oxy gen transfer rate so that the oxygen growth yield, Y-X/O2, remained at a constant value of 11 g dry weight of biomass/mol oxygen consumed. P ure oxygen had a positive effect on Leuconostoc growth. Oxygen transfe r was limiting under air, but pure oxygen provided bacteria with suffi cient dissolved oxygen and leuconostocs were able to consume large amo unts of oxygen. Acetate production increased progressively with oxygen consumption so that the total molar concentration of acetate plus eth anol remained constant. Maximal Y-X/S was obtained with a 120 1/h flow rate of pure oxygen: the switch from ethanol to acetate was almost: c omplete. In this case, a 46.8 g/mol Y-X/S and a 0.69 h(-1) maximal gro wth rate could be reached.