Electron acceptor availability alters carbon and energy metabolism in a thermoacidophile.

The thermoacidophilic Acidianus strain DS80 displays versatility in its energy metabolism and can grow autotrophically and heterotrophically with elemental sulfur (S°), ferric iron (Fe ³⁺ ) or oxygen (O ₂ ) as electron acceptors. Here, we show that autotrophic and heterotrophic growth with S° as the electron acceptor is obligately dependent on hydrogen (H ₂ ) as electron donor; organic substrates such as acetate can only serve as a carbon source. In contrast, organic substrates such as acetate can serve as electron donor and carbon source for Fe ³⁺ or O ₂ grown cells. During growth on S° or Fe ³⁺ with H ₂ as an electron donor, the amount of CO ₂ assimilated into biomass decreased when cultures were provided with acetate. The addition of CO ₂ to cultures decreased the amount of acetate mineralized and assimilated and increased cell production in H ₂ /Fe ³⁺ grown cells but had no effect on H ₂ /S° grown cells. In acetate/Fe ³⁺ grown cells, the presence of H ₂ decreased the amount of acetate mineralized as CO ₂ in cultures compared to those without H ₂ . These results indicate that electron acceptor availability constrains the variety of carbon sources used by this strain. Addition of H ₂ to cultures overcomes this limitation and alters heterotrophic metabolism.
(© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.)