Reduction of Fumarate to Succinate Mediated by Fusobacterium varium

Accumulation of succinate as a fermentation product of Fusobacterium varium was enhanced when the anaerobic bacterium was grown on complex peptone medium supplemented with fumarate. Residual substrates and fermentation products were determined by proton NMR spectroscopy. Cells collected from the fumarate-supplemented medium (8-10 h after inoculation) supported the conversion of fumarate to succinate when suspended with fumarate and a co-substrate (glucose, sorbitol, or glycerol). Succinate production was limited by the availability of fumarate or reducing equivalents supplied by catabolism of a co-substrate via the Embden-Meyerhof-Parnas (EMP) pathway. The choice of reducing co-substrate influenced the yield of acetate and lactate as side products. High conversions of fumarate to succinate were achieved over pH 6.6-8.2 and initial fumarate concentrations up to 300 mM. However, at high substrate concentrations, intracellular retention of succinate reduced extracellular yields. Overall, the efficient utilization of fumarate (≤ 400 mM) combined with the significant extracellular accumulation of succinate (corresponding to ≥ 70% conversion) indicated the effective utilization of fumarate as a terminal electron acceptor by F. varium and the potential of the methodology for the bioproduction of succinate.