Microbes Play Part in Oil Spill Clean Up

Hydrocarbons naturally enter the marine environment at cold seeps along continental shelves. Natural seeps are sporadic and can be diffuse or intense. The Gulf of Mexico is one of the most oil rich basins in the world, the 2010 Macondo blow out leaked 15 times more oil and gas than the Gulfs natural seeps. Microbial hydrocarbon degraders in marine environments (e.g. Alcanivorax spp. and Marinobacter spp.) work together to acts as a metabolic network: primary oil degraders produce surfactants to emulsify oil, secondary consumers intercept intermediate molecules (e.g. alcohols and alkenes) increasing molecules bioavailability to other organisms. This slick led to unprecedented changes in the marine environment and microbial populations. This review paper explores microbial responses to the deep water oil plume, surface slicks and sediment composition changes.

Native microorganisms responded rapidly until limited by environmental factors; increased archaea changed nitrifying microorganism community structure. During the lifetime of the oil plume the deep water bacterial community shifted and hydrocarbon degradation gene presence increased. 16s PCR showed the blow out caused gammaproteobacteria alkane degraders Oceanspirillales to dominate, between 2 and 4 weeks later communities shifted to mostly PAH degraders, Cycloclasticus and Colwellia. After 6 months, communities near the well head diversified to include alkane, PAH and methyl degraders (Methtlophilacaea, Methylococcaceae and Methylophaga). Despite the blowout being offshore and the majority of hydrocarbons being weathered before reaching coastal waters oil contamination on beaches affected microbial communities in a similar way to those in deep water. Oil contaminated sands contained up to 4 times the microbes in clean sands and followed similar assemblage changes to the deep water. Taxonomic diversity decreased in response to the pollution but rebounded a year later.

Sediments significantly changed, within a few weeks large aggregations of marine snow were observed which sunk and settled on the sea floor. Laboratory experiments showed the huge aggregations were due to increased cell densities, activities of carbohydrate degrading enzymes with the entrapment of oil droplets in an extensive matrix of polysaccharides characteristic of aromatics and alkane reducing bacteria. When deposited, aerobic oil degrading communities on the detritus were gradually replaced by anaerobic decomposers. 8 months after the spill the top 2cm of sediments local to the well showed 10-20% less organic carbon and nitrogen compared to underlying sediment nutrients are likely to have been consumed by pelagic and benthic microbiota.

This review article exploits a unique situation to link studies and build a view of microbial effects and habitats. In addition, lapses in knowledge can be identified: oil and gas are rarely accurately measured in the marine environment making it difficult to quantify oil degradation; marine snow provides a net to capture oil droplets, but we need to investigate what happens to them in the water column and on the seabed further; microbes are known to break down many hydrocarbon compounds (e.g. alkanes, PAHs, methane) but we need to quantify and assess more persistent compounds (e.g. tar).

Joye, S. B., Teske, A. P., Kostka, J. E. (2014) Microbial Dynamics Following the Macondo Oil Well Blowout across Gulf of Mexico Environments. BioScience. 64 (9): 766-777. http://bioscience.oxfordjournals.org/content/64/9/766.full