ANAEROBIC HYDROCARBON DEGRADATION

The middle of the 20th century saw an increase of investigation into microbial hydrocarbon degradation, mainly due to the increased production in oil which led to higher incidences of accidental leaks and spills. A large number of microorganisms have shown the ability to utilise hydrocarbons as the sole energy source in their metabolism. Given the high carbon content available for biomass production, and the high energy content of such highly reduced compounds, it is hardly surprising that many microbes have evolved or acquired the ability to utilise hydrocarbons as sources of carbon and energy. This degradation of hydrocarbons is effectively the ultimate natural mechanism for the removal of hydrocarbon pollutants from the environment. Claude Zobell (1946) was one of the first people to summarise the combined knowledge of microbial degradation of hydrocarbons.

Aerobic microorganisms usually initiate the metabolism of alkanes through monooxygenase reactions. The initial intracellular attack is an oxidative process which generates a highly reactive oxygen species. The incorporation of oxygen forms the key reaction in the activation of the hydrocarbon for degradation. In the late 80s studies started to implicate novel microbes capable of anaerobic hydrocarbon degradation. Since there is no biochemical agent under anoxic conditions with the same hydrocarbon activating properties as oxygen species when under anoxic conditions, these organisms seem to be able to activate hydrocarbons by unprecedented biochemical mechanisms, completely different than those described in aerobic hydrocarbon metabolism. This results in anaerobic activation reactions of hydrocarbons which are mechanistically unprecedented in biochemistry.

The understanding of the microorganisms and pathways involved in anaerobic hydrocarbon degradation is limited, but the availability of glycyl radical enzyme gene sequences (bssA, assA and macD) associated with anaerobic alkane metabolism enables the application of gene detection tools during environmental assessments and presents the additional opportunity to screen for the occurrence of anaerobic alkane degradation as well.