Bidirectional usage of ferulate by the acetogen Peptostreptococcus productus U-1: CO2 and aromatic acrylate groups as competing electron acceptors

The influence of CO2 on the ability of Peptostreptococcus) productus U-1 (ATCC 35244) to use an aromatic acrylate group as an energy-conserving electron acceptor during O-methyl-dependent growth was examined. Ferulate (a methoxylated phenylacrylate), unlike hydroferulate (a methoxylated phenylpropionate), supported growth under CO2-limited conditions. Two phases occurred during ferulate utilization in CO2-limited cultures. In phase I (maximum growth), O-methyl-derived reductant was coupled mainly to acrylate group reduction, and acetate synthesis (CO2 as reductant sink) was minimal. In phase II, acetate synthesis increased, but cell yields in this phase were much less than in phase I. In CO2-enriched cultures, distinct phases were not observed; reductant was coupled equally to CO2 and acrylate group reduction. Under CO2-enriched conditions, O-methyl and acrylate groups were incompletely metabolized, and molar growth yields were significantly lower compared to CO2-limited conditions. Resting cell studies indicated that O-demethylase and aromatic acrylate oxidoreductase activities were induced by ferulate. These findings demonstrated that P. productus U-1 can use the aromatic acrylate oxidoreductase system as a sole, energy-conserving, electron-accepting process, but is not able to prevent the simultaneous use of the bioenergetically less favourable acetyl-CoA pathway during O-methyl-dependent growth.