Assessing the impacts of light synthetic crude oil on microbial communities within Laurentian Great Lakes’ sediment habitats

The ability of microbial communities to respond to and degrade crude oil in marine environments is well understood, yet fewer studies have examined freshwater environments. The Laurentian Great Lakes are one of the world's largest surface freshwater sources. A pipeline that transports light synthetic crude oil crosses between two of the Great Lakes (the Straits of Mackinac, connecting Lakes Michigan and Huron, U.S.A.), and there is uncertainty on how the various habitats within this region would respond to accidental crude oil exposure. In this study, sediment microbial communities from three distinct habitats (coastal beach, freshwater coastal wetland, and Lake Michigan deep sediments) were used in microcosm experiments to document their community response (16S rRNA gene sequencing) to light synthetic crude oil (headspace gas chromatography). Microbial community structure (beta diversity) was impacted after exposure to crude oil in each of the habitats examined, with each habitat showing a different level of resistance to crude oil. Additionally, within each habitat, beta diversity distinguished sub-communities that increased in abundance in experimental treatments. Specifically, an increase in total abundance of Alphaproteobacteria, Betaproteobacteria, or Gammaproteobacteria was observed in microcosms exposed to crude oil regardless of habitat type. Methane, a potential hydrocarbon degradation byproduct, was observed in the headspace of the microcosms after exposure to crude oil, which may indicate methanogenic hydrocarbon degradation. These data suggest Great Lakes freshwater microbial communities will respond differently to crude oil exposure but may have shared community members involved in resisting and degrading light synthetic crude oil.