Effect of Sophorolipid Biosurfactant on Oil Biodegradation by the Natural Oil-Degrading Bacteria on the Weathered Biodiesel, Diesel and Light Crude Oil

This study investigated the role of natural oil-degrading bacteria in the weathered biodiesel (BD), diesel (D) and light crude oil (L) in oil biodegradation in seawater with and without sophorolipid biosurfactant. Mixtures of artificial seawater and weathered oil with and without sophorolipid dispersant were incubated at 22 ± 1°C and 100 rpm for 28 days. Analysis of the remaining of total petroleum hydrocarbons showed degradation of 43 ± 0.7%, 45 ± 5.7% and 39 ± 4.6% of biodiesel, diesel and light crude oil, respectively, during the natural biodegradation and 44 ± 5%, 47.5 ± 3.9% and 44 ± 1% of biodiesel, diesel and light crude oil, respectively, with sophorolipid by the existing bacteria after 28 days. Characterization of bacteria isolated from the BD, D and L oil by 16S rRNA pyrosequencing showed that the Firmicutes was the dominant phylum in biodiesel (100%) and diesel (53%). The Actinobacteria was dominant in the diesel (47%) and the Proteobacteria (97%) and Actinobacteria (3%) were the two dominant phyla in the light crude oil. The hydrophobicity results showed that the bacteria consumed the hydrocarbons mainly by changing their cell surface structures in the natural biodegradation treatment and increase in the micellar dispersion of hydrocarbons in the biodegradation treatment with the sophorolipid. This study confirmed the significant contribution of natural bacteria in the weathered diesel, biodiesel and light crude oil in the biodegradation and the positive effect of sophorolipid on the biodegradation