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-conserv ing electron acceptor during O-methyl-dependent growth was examined. F erulate (a methoxylated phenylacrylate), unlike hydroferulate (a metho xylated phenylpropionate), supported growth under CO2-limited conditio ns. Two phases occurred during ferulate utilization in CO2-limited cul tures. In phase I (maximum growth), O-methyl-derived reductant was cou pled 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 c oupled equally to CO2 and acrylate group reduction. Under CO2-enriched conditions, O-methyl and acrylate groups were incompletely metabolize d, and molar growth yields were significantly lower compared to CO2-li mited conditions. Resting cell studies indicated that O-demethylase an d aromatic acrylate oxidoreductase activities were induced by ferulate . These findings demonstrated that P. productus U-1 can use the aromat ic acrylate oxidoreductase system as a sole, energy-conserving, electr on-accepting process, but is not able to prevent the simultaneous use of the bioenergetically less favourable acetyl-CoA pathway during O-me thyl-dependent growth.