Anaerobic biodegradation of hydrocarbons including methane

Abstract

Hydrocarbons are highly abundant in nature, originating from both, geochemical and biological processes. Because of the low reactivity of their C-H bonds, either aliphatic or aromatic, hydrocarbons are usually hard to degrade biologically, and all known aerobic hydrocarbon-degrading organisms overcome this reactivity barrier by involving oxygen-dependent mono- or dioxygenases for the initial attack at the hydrocarbons. It was surprising when about 20 years ago biological hydrocarbon degradation was shown to occur also in the absence of molecular oxygen. In the meantime, many hydrocarbons are known to be degraded anaerobically by a large variety of facultatively or strictly anaerobic bacteria. These bacteria initiate their metabolic pathways by oxygen-independent hydrocarbon-activating reactions that are completely different and much more divergent than the aerobic initial reactions and represent novel biochemical principles. We review here the current knowledge on the ecology of anaerobic hydrocarbon degraders and their habitats, introduce the organisms involved, and describe the biochemical pathways and enzymes allowing these remarkable properties. Finally, we discuss some implications of these new insights on possible applications.