Substrates, acetogenic

Acetogens can also use a diverse number of terminal electron acceptors substrates (Drake 1994 Drake et al. 1997) these acceptors and the resulting reduced end products include ... 

In an effort to establish the nature of the acetogenic substrates, raw sludge was separated into solids and supernatant fractions and were tested individually as substrates in the digesting sludge. Most of the substrates responsible for the rapid formation of acetate were found in the water-soluble solids fraction (Figure 3), and no acetogenic activity was observed in the supernatant fractions. 

Further fractionation of the solids was effected by extraction with a chloroform-methanol mixture to separate the lipids. The control sludge and the fractions were tested for acetogenic activity at twice their normal equivalent sludge concentrations to ensure production of measurable quantities of acetic acid. The data plotted in Figure 4 indicate that the lipid fraction contains the substrates responsible for the rapid increase in acetate following addition of raw sludge. Acetate increased at approximately the same rate as the raw sludge control. No acetate was observed... 

FIGURE 12.1 Routes to methane by anaerobic digestion of complex substrates. Bracketed letters denote mixed cultures of bacteria F, fermentative A, acetogenic M, methanogenic. From Zehnder, Ingvorsen, and Marti (1982). 

There has been considerable interest in the anaerobic degradation of propionate that is a fermentation product of many complex substrates, and syntrophic associations of acetogenic and metha-nogenic bacteria have been obtained. 

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