Anaerobic respiration using Fe3+, S0, and H2 in the chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans

The chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans has been known as an aerobe that respires on iron and sulfur. Here we show that the bacterium could chemolithoautotrophically grow not only on H-2/O-2 under aerobic conditions but also on H-2/Fe3+, H-2/S-0, or S-0/Fe3+ under anaerobic conditions. Anaerobic respiration using Fe3+ or S-0 as an electron acceptor and H-2 or S-0 as an electron donor serves as a primary energy source of the bacterium. Anaerobic respiration based on reduction of Fe3+ induced the bacterium to synthesize significant amounts of a c-type cytochrome that was purified as an acid-stable and soluble 28-kDa monomer. The purified cytochrome in the oxidized form was reduced in the presence of the crude extract, and the reduced cytochrome was reoxidized by Fe3+. Respiration based on reduction of Fe3+ coupled to oxidation of a c-type cytochrome may be involved in the primary mechanism of energy production in the bacterium on anaerobic iron respiration.