The Growth Yield of Desulfovibrio desulfuricans M6 on Different Substrates

Growth yield of Desulfovibrio desulfuricans M6 was measured using different substrates. The cell yield of fermentative growth on pyruvate was 6.22 g cell $mol^{-l}$ pyruvate. Since 1 ATP is available from substrate-level phosphorylation from the oxidation of pyruvate to acetate, $Y_{ATP}$ of the bacterium should be the same as $Y_{pyruvate}$ (6.22 g cell $mol^{-l}$ ATP). The cell yields of the bacterium on different electron donors were measured with sulfate as the electron acceptor. Cell yields on lactate, pyruvate and $H_2$ were 9.39, 13.76 and 8.45 g cell $mol^{-l}$ substrate, respectively. From these figures ATP available from electron-transport phosphorylation (ETP) of the electron donors used was calculated. ATP produced by ETP of each electron donnor were 1.71 from pyruvate, 1.51 from lactate and 1.76 from $H_2$. These values show that electrons from the oxidation of lactate to pyruvate are consumed to reduce sulfate through a reverse electron transport mechanism requiring 0.2 ATP for each pair of electrons. Based on these results, discussions are made on the electron transport mechanism in the bacterium.