Aerobic cultivation of Streptococcus zooepidemicus and the role of NADH oxidase

Abstract

A metabolic flux model was developed for Streptococcus zooepidemicus to compare the metabolism of glucose and maltose during aerobic batch cultivation. Lactic acid was the main product of glucose metabolism whereas acetic acid was the main product of maltose metabolism. This difference was chiefly attributed to the two-fold higher flux through NADH oxidase in maltose-grown cells that enabled the ATP generation rate to remain high despite a slower maltose consumption rate. The two-fold higher flux was matched by a two-fold increase in NADH oxidase activity, 2.53±0.1 μmol NADH min −1 mg −1 protein on maltose versus 1.07±0.04 μmol NADH min −1 mg −1 protein on glucose, indicating that NADH oxidase activity is regulated by the energy status of the cell. Surprisingly, the energy status of the cell had little impact on hyaluronic acid (HA) yield and molecular weight.