Discrimination byparacoccus denitrificans between (6-13C)glucose and (1-13C)glucose as carbon substrates for growth: An investigation using gas chromatography/mass spectrometry

Paracoccus denitrificans was grown with either (1-13C) glucose or (6- 13C)glucose as the sole carbon source for growth and the extracts were analysed by gas chromatography/mass spectrometry. The distribution of label observed in the metabolites confirmed that the Embden-Meyerhof pathway was not active in vivo whereas the Entner–Doudoroff and pentose phosphate pathways were operative. However, the pattern of 13C labelling observed in extracts of cells grown on (6-13C) glucose also indicated that a third major glucose oxidation pathway was operative in Paracoccus in addition to the Entner-Doudoroff and pentose phosphate pathways already detected. This additional glucose oxidation pathway decarboxylates the bexose unit in the C-6 position, and is designated the “G6” pathway. It is proposed that the enzymes of the glucuronic acid cycle are used for this decarboxylation sequence. The relative fluxes of glucose carbon through the Entner–Doudoroff, pentose phosphate and G6 pathways calculated for Paracoccus grown on (1- 13C)glucose were substantially different from those calculated for growth on (6-13C)glucose.