Biodegradation of petroleum oil in cold marine environments

Abstract

The cold regions of the Earth are exposed to petroleum oil exploration, production, and transport, with risk of oil spills. Biodegradation is an essential petroleum weathering process and may remove discharged petroleum compounds completely by mineralization processes. These processes are most apparent for soluble compounds and with dispersed oil. Surface and subsurface spills will generate different situations, and in addition freezing of oil in marine ice may transport the oil over large distances. A variety of marine psychrophilic or psychrotolerant bacteria from both shallow and deepwater environments have been reported to degrade hydrocarbons in seawater or marine sediments, most of these affiliated within the phyla Proteobacteria and Bacteroidetes. Several of these may also act on hydrocarbons in sea ice, and active bacterial respiration in sea ice has been shown down to temperatures of -20 °C. The cold environments require several microbial survival and catabolism strategies, including productions of exopolysaccharides, cold-active enzymes, cold-shock, cold-acclimation and antifreeze proteins, as well as adjusting their membrane lipid composition. Oil biodegradation in cold environments is well documented by laboratory and field studies, and even oil frozen in marine ice will stimulate bacterial metabolism. Flocculation processes have also been associated with oil biodegradation, raising discussions on the fate of the oil, especially after the Deepwater Horizon blowout. Bioremediation in cold marine environments has been investigated as a labor-effective technology which generates no harmful by-products, mainly by adding fertilizers to stimulate the oil biodegradation by the indigenous bacteria (biostimulation), but also inoculation of exogenic hydrocarbonoclastic cultures (bioaugmentation) has been suggested.