Abstract
Summary 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.