Considerations on the energy metabolism of Clostridium kluyveri.

Abstract

On the basis of the known fermentation balance and of the enzyme activities reported in Clostridium kluyveri the ethanol-acetate fermentation of Clostridium kluyveri has been analyzed with respect to possible ATP-yielding reactions and to the significance of the evolution of hydrogen gas during the fermentation. The fermentation pathway presented allows the following conclusions: hydrogen gas is an essential end product of the ethanol-acetate fermentation. For each two moles of hydrogen gas evolved one mole of acetyl coenzyme A becomes available to the cells for ATP synthesis, and it is not necessary to assume that ATP is synthesized by Clostridium kluyveri by electron transport phosphorylation. Hydrogen gas must be formed in the dehydrogenation of acetaldehyde. Since Clostridium kluyveri contains a NAD reductase, less than one mole of hydrogen gas is formed per mole of acetaldehyde oxidized, thus explaining that acetate is required for the fermentation of ethanol. It could be demonstrated that growth of Clostridium kluyveri is slow in a hydrogen atmosphere as compared with growth in an argon atmosphere. The general fermentation equation constructed is in accordance with the experimental data of Bornstein and Barker and of Thauer et al.