Anaerobic Respiration Using Fe ³⁺ , S ⁰ , and H ₂ in the Chemolithoautotrophic Bacterium Acidithiobacillus ferrooxidans

Abstract

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 /Fe 3؉ , H 2 /S 0 , or S 0 /Fe 3؉ under anaerobic conditions. Anaerobic respiration using Fe 3؉ 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 Fe 3؉ 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 Fe 3؉ . Respiration based on reduction of Fe 3؉ 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.Acidithiobacillus ferrooxidans is generally accepted to be an aerobic chemolithoautotroph that derives energy for growth from oxidative respiration involving the oxidation of ferrous iron or various sulfur compounds. Brock and Gustafson reported that the bacterium reduces Fe 3ϩ in the presence of S 0 (10). However, the reduction was not recognized as respiratory reactions since iron reduction did not permit growth of the bacterium (39). Therefore, it was accepted that coupling reduction of Fe 3ϩ to oxidation of S 0 was one of the steps in the sulfur metabolism by the bacterium (39). Pronk et al. (32,33) and Das et al. (12) showed that the bacterium grew on the oxidation of S 0 by Fe 3ϩ under oxygen-limited conditions. Although these findings raised the possibility that A. ferrooxidans might be able to grow under anaerobic conditions, the aforementioned enzymatic activity was not accompanied by growth (39), and it is still unclear whether Fe 3ϩ serves as an electron acceptor for anaerobic respiration. On the other hand, the bacterium would grow on hydrogen under aerobic conditions (14). In that case, H 2 served as the electron donor enabling an oxidative respiratory chain to derive energy for chemolithoautotrophic growth.On the other hand, in many facultative heterotrophs in both Archaea and Bacteria, anaerobic respiration involving reduction of Fe 3ϩ or S 0 is typically coupled to the oxidation of H 2 (25,26,30,38,42). One of the principle roles of such respiration would have been to support energy for chemolithoautotrophy (34), a type of autotrophy that typically served as the growth mode of such facultative heterotrophs in Archaea and Bacteria as hyperthermophilic archaebacteria, sulfur-reducing bacteria, and primitive fermentative bacteria (18, 24, 36-38, 42, 44). However, little is known about the role played by anaerobic respiration involving Fe 3ϩ or S 0 reduction in the growth of typical, known chemolithoautotrophic bacteria, which include a variety of sulfur, iron, ammonia, and nitrite oxidizers. We have found tha...

Acidithiobacillus ferriphilus sp. nov., a facultatively anaerobic iron- and sulfur-metabolizing extreme acidophile

“…None of the A. ferriphilus strains examined grew aerobically on hydrogen. This is also the case for most strains of A. ferrivorans, although all strains of A. ferrooxidans and A. ferridurans examined have been shown to grow by coupling the oxidation of hydrogen to the reduction of either molecular oxygen or ferric iron (Ohmura et al, 2002;Hedrich & Johnson, 2013b).…”

Respiratory gene clusters of Metallosphaera sedula – differential expression and transcriptional organization

“…The predominantly accepted view of the role of micro-organisms in the solubilization of metal sulfides is that they provide protons from the oxidation of sulfur compounds and maintain iron in its oxidized form for Fe 3+ /H + attack on the mineral (Sand et al, 2001). Over three decades of research on mesophilic bacteria such as A. ferrooxidans has led to an understanding of the organization of the electron transfer chain in this chemolithoautotroph (Brasseur et al, 2002;Ohmura et al, 2002).…”

Microbial community study of the iron ore concentrate of the Sishen Iron Ore Mine, South Africa

“…A. ferrooxidans is acknowledged as being responsible for iron and inorganic sulphur compound oxidation in areas such as mine tailings and coal deposits (Horan 1999). A. ferrooxidans is assumed to be obligately aerobic, however, under anaerobic conditions it can be grown on elemental sulphur using ferric iron as an electron acceptor (Das et al 1992;Pronk et al 1992;Ohmura et al 2002). It has been documented that At.…”