Simplified scheme of propionate metabolism in Veillonella spec.: In contrast to Propionibacterium spec., in Veillonella spec. there is no transcarboxylase . The transcarboxylation is realized via a pyruvate-carboxylase and a methyl-malonyl-CoA-decarboxylase. This is less energy efficient. 1 mol ATP is consumed by the pyruvate-carboxylation, two third can be recovered by the fumarat-reduction, one third via methylmalonyl-CoA-decarboxylation. As in the acryloyl-pathway there is no net ATP production. The regeneration of NADH2 to NAD can be realized by hydrogen production, which is more energy efficient (Denger and Schink (1992)).