Rhamnolipid Biosurfactants Enhance Microbial Oil Biodegradation in Surface Seawater from the North Sea

This study provides strong evidence thatthe biosurfactantrhamnolipid is more efficient than the widely used chemical dispersantsCorexit 9500 and Slickgone NS in stimulating oil biodegradation innatural seawater. Biosurfactants arepromising alternatives to chemical dispersantsfor combating marine oil spills; however, the impacts of biosurfactantson microbial community composition and oil biodegradation activitiesremain largely unknown. Here, we conducted a time-course microcosmexperiment mimicking oil spill scenarios with surface seawater fromthe North Sea, amended with either the biosurfactant rhamnolipid ora dispersant (Corexit 9500 or Slickgone NS). Radioactive tracer assaysto track hexadecane and naphthalene oxidation as well as bacterialproduction revealed the highest hydrocarbon oxidation rates and generalmicrobial activities in the rhamnolipid-amended oil microcosms, followedby oil microcosms with Slickgone and Corexit. Impacts on the microbialcommunity composition differed among treatments, and growth of oil-degrading Colwellia was stimulated remarkably in Corexit-amended oiland oil-only microcosms, while potential oil-degrading Oleispira were highly enriched in the presence of oil in combination withrhamnolipid or Slickgone. Furthermore, increased abundances of Colwellia and Oleispira, and stimulatedbacterial production in microcosms with only rhamnolipid, Corexit,or Slickgone, indicated their involvement in biosurfactant/dispersantbiodegradation. Our findings highlight varying microbial impacts resultingfrom rhamnolipid and chemical dispersants and suggest great promisefor the application of biosurfactants in future marine oil spills.