Influence of constant and oscillating dissolved oxygen concentrations on keto acid production by Gluconobacter oxydans subsps. melanogenum.

Gluconobacter species are known to oxidise glucose via a direct oxidation pathway which is distinct from the pentose phosphate pathway. In the present communication results of an investigation on the influence of different dissolved oxygen concentrations (DO) on the production of 2,5-diketogluconic acid in batch and chemostat cultures are given. DO of 30% relative to air at 1 bar was found as a threshold level for optimum productivity. The positive influence of continuous availability of dissolved oxygen on the process of rapid glucose oxidation was unambiguously shown as the result of induction of membrane bound dehydrogenases involved in direct glucose oxidation. Furthermore data of scale-down experiments in which the organism was cultivated under oscillations of dissolved oxygen, are given. The influences of such oscillations of DO in the region of the established threshold (30% saturation) were found to result in a prolonged lag phase for growth and product formation. The data obtained in this study revealed critical residence times at low DO that could be employed as a criterion for scale up of this aerobic process.