A microbial seedbank from a natural oil seep accelerates hydrocarbon degradation in freshwater oil spills

BackgroundAnthropogenic oil spills contribute largely to global hydrocarbon pollution on land and water. Freshwater oil spills are understudied compared to marine oil spills despite its importance. However, if degradation rates of such anthropogenic oil spills could be increased before reaching susceptible habitats, harmful effects of toxic hydrocarbons could be mitigated. We hypothesized that microorganisms from freshwater natural oil seeps are well adapted to utilize crude oil as a sole carbon source and could be applied as a seedbank to accelerate the degradation of anthropogenic oil slicks in freshwater ecosystems.Microcosm experiments were conducted with water and heavy crude oil from a natural oil seep in Haenigsen, Germany. Light crude oil, and river water naive to oil were utilized to mimic an anthropogenic oil spill in a naive environment. Seven test conditions with different water (adapted and naive) and oil types (heavy, light oil, both oils mixed 1:1) were produced to test our hypothesis. Oil degradation was monitored over 81 days with reverse stable isotope labeling, pH measurement and cell counting. Microbial community composition was analyzed with 16S rRNA gene amplicon sequencing in the beginning and end of the experiment.ResultsMicrobial communities were different from each other depending on the treatment. Reverse stable isotope labeling revealed that oil mineralization rates in microcosms with adapted microbes were overall increased. In mixed oil incubations, simulating the application of a microbial seedbank on anthropogenic spills, degradation rates were 0.26 mM day-1 with microbes from the adapted water and 0.15 mM day-1 in naive water set-ups. Applying the natural seep oil slick as a microbial seed bank to the light oil slick in naive water enhanced hydrocarbon mineralization by 32%.ConclusionSpeeding up the natural weathering processes of oil pollutions is very beneficial to mitigate the severeness of an oil spill. If detrimental effects from microbial seedbanks applied in their natural oil slick matrix can be ruled out, then microbial seedbank from natural oil seeps could be an invaluable instrument for oil spill countermeasures.