All oil spills are not created equally: A view from the bacterial world

Investigations of the relationships between crude oil and bacterioplankton have provided clues into how crude oil constituents are degraded, and how anthropogenic spills affect system nutrient cycling and food webs. The Deepwater Horizon oil spill in 2010 re-invigorated the investigation of how marine bacteria respond to oil spills. While much of the historical research and initial efforts focused on the biodegradation of oil, it became quickly apparent that much of the bacterial community was affected negatively by oil. Environmental conditions often altered those responses.  Herein we present a summary of results, both published and unpublished, indicating that based on the bacterial responses to oil, it is difficult to produce universal conclusions on the effects of oil spills on marine bacterial communities, confounding both the impacts of the spills, but also the best response to mitigate the effects. In the northern Gulf of Mexico, summer was the worst time to have a spill, but also when Deepwater Horizon occurred. Exposure to sunlight created a myriad of responses depending on the duration and spectral quality of that exposure, but was also dependent on the source of the oil. Those that generated the greatest inhibition to community growth, also produced the greatest changes in bacterial community structure, including variability in known oil degrading bacterial groups. Responses were altered even more when clean-up methods were included in the analyses. The use of Corexit 9500A in combination with oil and sunlight increased the stress response of bacteria. While burning oil reduced some toxic components of oil, subsequent exposure to sunlight increased the toxic response. These results indicate that microbial responses to oil spills are dependent on the source of the oil, solar conditions, and the time and location of the spill complicating the ability to predict oil spill effects.