Crude oil can naturally seep to the Earth's surface, releasing oil into various ecosystems and forming oil slicks. Although oil is toxic to most life, some bacteria can use oil as carbon source and degrade it. Natural and anthropogenic oil slicks differ in their biological, chemical, and physical properties, yet natural seeps remain understudied from a microbiological perspective. Oil spills contribute largely to global hydrocarbon pollution and natural weathering is often the best choice for oil spill countermeasures in sensitive ecosystems like marshes and coral reefs, where physical cleanup could cause more damage. Accelerating weathering of anthropogenic oil spills before they reach vulnerable habitats could ultimately minimize ecosystem damages.
We hypothesized, that oil degradation is faster in natural oil films compared to recently introduced oil films and that adapted microorganisms, isolated from natural oil seeps, can accelerate anthropogenic oil slick weathering.
To study our hypotheses, water and heavy oil from a natural oil seep in Germany and from oil-unaffected river water were sampled, microorganisms are considered as adapted and naïve, respectively. Microcosm experiments were conducted to compare oil degradation rates between adapted, naïve and mixed microbes, treated with light and heavy oil. Oil biodegradation was monitored over 153 days by pH-measurements, cell counting, CO2-deveolopment by reverse stable isotope labeling (RSIL) and changes in the microbial community composition via 16S rRNA gene amplicon sequencing. A pH decrease was observed for all test conditions and aligned with the amount of produced CO2. Adapted microbes demonstrated up to 5x faster degradation rates of light oil compared to the naïve microbes. In mixed oil incubations, simulating the application of adapted microbes to anthropogenic spills, degradation rates were 0.26 ± 0.01 mM/day with microbes from the adapted water and 0.15 ± 0.02 mM/day in naïve water microcosms, resulting in 58% higher degradation rates.
Natural oil seeps can serve as a valuable source of oil degrading microbial communities that can be used as seedbanks for accelerated hydrocarbon degradation, especially in anthropogenic oil spill scenarios where oxygen is not a limiting factor.