ABSTRACT
Abstract In many anaerobic ecosystems, a consortium of microorganisms rather than a single species is the catalytic unit responsible for biodegradation. Interspecies hydrogen and formate transfer are critical in regulating the flow of carbon and electrons in many anaerobic ecosystems. Anaerobes use novel approaches such as the addition of fumarate or a carboxyl group to activate hydrocarbons, the hydrolysis of ATP to provide low potential electrons to reduce aromatic rings, and oxidation-reduction or cofactor B i2-mediated reactions to generate free radicals for dehydration reactions. In addition to fermentative metabolism where ATP production occurs mainly by substrate-level phosphorylation, anaerobes can use diverse inorganic or organic compounds as electron acceptors. Anaerobic respiratory chains use redox loops, redox-driven pumps, and the separation of proton-consuming and protonproducing reactions across the membrane to generate a chemiosmotic potential. Some anaerobes can generate a chemiosmotic potential by the electrogenic efflux of compounds across the membrane. The dependence of anaerobes on low potential and free radical biochemistry makes them very sensitive to oxygen. The degree to which an anaerobe depends on oxygen-sensitive systems relative to its ability to detoxify reactive oxygen compounds determines its oxygen tolerance.
