The influence of CO on the ability of U-1 (ATCC 35244) to use an aromatic acrylate group as an energy-conserving electron acceptor during -methyl-dependent growth was examined. Ferulate (a methoxylated phenylacrylate), unlike hydroferulate (a methoxylated phenylpropionate), supported growth under CO-limited conditions. Two phases occurred during ferulate utilization in CO-limited cultures. In phase I (maximum growth), -methyl-derived reductant was coupled mainly to acrylate group reduction, and acetate synthesis (CO 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 CO-enriched cultures, distinct phases were not observed; reductant was coupled equally to CO and acrylate group reduction. Under CO-enriched conditions, -methyl and acrylate groups were incompletely metabolized, and molar growth yields were significantly lower compared to CO-limited conditions. Resting cell studies indicated that -demethylase and aromatic acrylate oxidoreductase activities were induced by ferulate. These findings demonstrated that 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 -methyldependent growth.


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