Central carbon metabolism and respiration in Gluconobacter oxydans

Abstract

Gluconobacter oxydans, an α-proteobacterial species used for industrial vitamin C production, possesses a number of unusual metabolic features. Because of the absence of phosphofructokinase, succinyl-CoA synthetase, and succinate dehydrogenase, the Embden-Meyerhof-Parnas pathway (EMP) and the tricarboxylic acid (TCA) cycle are interrupted, leaving the pentose phosphate pathway (PPP) and the Entner-Doudoroff pathway (EDP) as the only complete pathways in central metabolism. Mutant and 13C-based carbon flux analysis revealed the PPP to be of prime importance for the cytoplasmic catabolism of sugars and derivatives. Pyruvate is partially converted to the end product acetate by pyruvate decarboxylase and acetaldehyde dehydrogenase. The respiratory chain involves two terminal ubiquinol oxidases, cytochrome bo3 and a cyanide-insensitive bd-type oxidase CIO. Mutant studies disclosed the paramount role of cytochrome bo3 for growth. In addition, a cytochrome bc1 complex and cytochrome c are present, but presumably no functional cytochrome c oxidase. A mutant lacking cytochrome bc1 showed a growth defect at acidic pH; nevertheless, the precise role of this complex remains to be clarified. Here we present an overview on recent studies concerned with central carbon metabolism and respiration in G. oxydans and also discuss corresponding data for species of Acetobacter and Gluconacetobacter.