Natural attenuation of spilled crude oil by cold-adapted soil bacterial communities at a decommissioned High Arctic oil well site.

Romulus C-42 is a decommissioned oil well on Ellesmere Island in the Canadian High Arctic, and is the northernmost well to have produced oil and gas anywhere in the world. The remote site has been untouched since a crude oil spill in 1972, offering a rare opportunity to examine natural attenuation in Arctic soils >40 years after a pollution event. Bacterial community composition in crude oil contaminated soils was significantly different from adjacent background soils. Two members of the genus Rhodanobacter (Alphaproteobacteria) were found consistently in contaminated soils, whereas two members of the genus Sphingomonas (Gammaproteobacteria) appeared opposite to each other, one consistently within the oil contaminated soil and the other consistently in non-oil contaminated soils. GC of soil hydrocarbon extracts revealed moderate levels of biodegradation relative to the original oil produced in 1972. Despite conditions permissive for bacterial activity (>0 °C) being limited to only a few months each year, natural attenuation by cold adapted soil microbial communities has taken place since the oil spill over 40 years ago. Rhodanobacter and Sphingomonas lineages are associated with contaminated and baseline conditions in this extreme environment, revealing the utility of bacterial diversity measurements for assessing long-term responses of Arctic soils to pollution. ORIGINALITY-SIGNIFICANCE STATEMENT: Romulus C-42, the northernmost onshore drilling well in the world, was decommissioned following a small crude oil spill in 1972. Soil bacterial diversity profiles obtained >40 years later revealed significant differences in oil contaminated soils relative to adjacent non-oil contaminated background soils, consistent with evidence for moderate biodegradation of spilled crude oil having taken place since 1972. The results indicate that microbial diversity profiling is an effective tool for assessing natural attenuation in remote High Arctic soils with a history of oil pollution.