Only a part of acetate is formed directly during fermentation. Most of it is formed by synthrophic reactions (Mclnerney 1999). Until now, only a few cultures have been isolated which are capable of this.
Synthrophobacter wolinii was described by Boone and Bryant (1980) and is able to convert propionate to acetate.
Synthrophomonas wolfeii was first described by Mclnerney et al. (1979). Butyrate is transformed to acetate:
CH3CH2CH2COO- + 2 H2O ^ 2 CH3COO- + H+ + 2 H2 AGo = 48.1 kJ mol-1
In both reactions hydrogen is formed. However, problems arise at higher H2 concentrations, as discussed in Section 8.1.3.
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