Carbon and Energy Flow during Acetogenic Metabolism of Unicarbon and Multicarbon Substrates

Abstract

In anaerobic environments carbon and energy flow is even more closely, interrelated than in aerobic habitats. This is due to the high proportion of carbon substrate transformed to fermentation end-products in order to create the necessary energetic balance for efficient cell growth. Some of these fermentation metabolites play an essential role in energy (ATP) production via substrate level phosphorylation reactions, while others can be viewed as electron sinks to avoid accumulation of excess reducing equivalents (as reduced co-enzymes). In an established multi-species population the product of one species fermentative metabolism will contribute to the substrate requirements of co-existing species. Thus, an essential interspecies carbon flow will occur involving various different metabolic types. In addition, some species that overcome their excess reducing equivalent yield via hydrogen gas production will almost certainly be present. This source of reducing power is essential for homoacetogenic and methanogenic autotrophs that fix carbon dioxide as principle substrate.