Effect of dispersants and biosurfactants on crude oil biodegradation and microbial ecology

One widely practised strategy to clean up oil spills is the application of surfactants that reduce the interfacial tension between oil and water, dispersing oil droplets into the water column. Understanding the effects of surfactants on the development of oil-degrading microbial communities is vital to understand their efficacy. Three biosurfactants (rhamnolipid, trehalolipid, sophorolipid) and three commercial dispersants (Finasol OSR 52, Slickgone NS, Superdispersant 25) were tested in North Sea microcosms contaminated with Norwegian Geochemical Standard, North Sea Oil (NSO-1), using 16S rRNA and ITS qPCR and amplicon libraries. Dispersant and biosurfactant treatments (excluding sophorolipid) saw significant bacterial 16S rRNA gene abundance growth after one day (16-fold; P<0.001), driven by obligate hydrocarbonoclastic bacteria (OHCB) genera (maximum of 34-fold; P<0.05), in comparison to the oil-only control. This growth translated into significant n-alkane degradation after one day (20 – 38%; P<0.05). Increases from operational taxonomic units (OTUs) within the genera's Oleispira and Thalassolituus were observed after one and three days. After seven days they decrease in abundance as OTUs within the genera's Alcanivorax and Cycloclasticus became dominant. The results of this study suggest that most surfactants significantly decrease the lag-phase of bacterial growth following oil contamination, as they increase hydrocarbon bioavailability allowing bacteria