Microbial degradation of hydrocarbons in the marine environment, with a focus on the microbial response to the Deepwater Horizon oil spill

The release of petroleum hydrocarbons into marine environments can occur naturally as well as through anthropogenic activities. The entry of hydrocarbons in the environment can lead to changes in microbial communities, with some microorganisms positively responding to and playing an important role in the degradation of the hydrocarbons. Deepwater Horizon (DwH) is recognised as the United State’s worst oil spill disaster, having had significant detrimental consequences to marine life in the Gulf of Mexico and the economies that depend on them. The application of sophisticated microbial and molecular techniques, such as stable isotope probing (SIP), next-generation sequencing methods and single-cell genomics, has provided an in-depth and holistic picture on the microbial response, its evolution over the course of the spill, and the role these organisms played in the fate of the oil during the DwH spill. In this review, an overview of evidence-based research on this is presented. Some of the typical hydrocarbon-degrading bacterial suspects were found enriched during the spill, whereas the enrichment of other unexpected species, such as Colwellia, became a focus of many studies, including having a role in the degradation of the chemical dispersant, Corexit, that was used to combat the spill. The literature highlights a number of factors that can limit the progress of hydrocarbon biodegradation in situ and that certain bacteria encode mechanisms to overcome unfavourable conditions. Also discussed are some of the conflicting reports relating to the toxicity and effectiveness of the chemical dispersant used, and the interest to develop bio-based dispersants.