Anaerobic Respiration

Abstract Many prokaryotes, Bacteria as well as Archaea, can obtain energy for growth in the absence of oxygen by anaerobic respiration. In this process, electrons are transferred to electron acceptors such as nitrate, sulfate, elemental sulfur, carbon dioxide, oxidized metal ions such as Fe(III) and Mn(IV) and a range of other compounds including fumarate, dimethylsulfoxide, trimethylamine N ‐oxide, arsenate and selenate. In all these processes, respiratory electron transport is coupled to the generation of a transmembrane proton gradient and the formation of adenosine triphosphate (ATP). Anaerobic respiration processes are seldom encountered in eukaryotic organisms. Anaerobic respiration has an important impact on the cycle of matter in nature, including processes such as denitrification (dissimilatory reduction of nitrate and nitrite to gaseous nitrogen), dissimilatory sulfate reduction with the formation of sulfide, the formation of methane and acetate from carbon dioxide and different processes in the biogeochemical cycles of metals. Key concepts When oxygen is not available for respiration many prokaryotes can use alternative electron acceptors to obtain energy by respiration. Anaerobic respiration is widespread in the two domains of prokaryotes: the Bacteria and the Archaea. Some prokaryotes can perform both aerobic and anaerobic respiration; others are obligate anaerobes that cannot use oxygen as electron acceptor for respiration. Denitrification, or dissimilatory reduction of nitrate to gaseous nitrogen, is an important process in the global nitrogen cycle. In anaerobic environments sulfate serves as terminal electron acceptor and is reduced to sulfide, giving rise to both the formation of metal sulfides in sediments and the evolution of hydrogen sulfide gas. Carbon dioxide is used as terminal electron acceptor by methanogenic Archaea for energy generation, yielding methane as final product and by different groups of prokaryotes to produce acetate. Anaerobic respiration processes are involved in a wide range of reactions involving oxidized ions of metals (iron, manganese, chromium, uranium and others) and metalloids (arsenic, selenium). Anaerobic respiration has important economic implications, both favourable (e.g. conversion of bound nitrogen to nitrogen gas in water purification plants) and unfavourable (e.g. loss of available nitrogen in agricultural soils, corrosion of steel pipes mediated by sulfate‐reducing bacteria).