Biofilm Formation by Hydrocarbon-Degrading Marine Bacteria and Its Effects on Oil Dispersion

Biodegradation of oil by marine bacteria is a significant pathway to oil spill remediation. Marine hydrocarbon degrading bacteria are known to form biofilms consisting of exopolymer and interconnected bacterial cells. This work indicates that microbial biofilm aids in the stabilization of dispersed oil droplets through the formation of biofilm at the oil–water interface and is therefore an environmentally benign and sustainable method to aid dispersion of spilled oil. Using a model hydrocarbon degrading organism Alcanivorax borkumensis, we show, through a combination of optical and high-resolution cryogenic scanning electron microscopy, that these microbes sequester into biofilm at the oil–water interface. We show that the bacterial culture incubated for 3 days and containing biofilm can disperse oil slicks moderately well (40–50%) as estimated by the baffled flask test and can thus be used as an environmentally benign response to oil spills. The dispersion occurs through bacterial adsorption at the oil–water interface together with the aid of naturally secreted biosurfactants that lower the oil–water interfacial tension by a factor of 2 to around 23 mN/m. When the bacterial culture is incubated for a week, the presence of biofilm at the interface can have a hindering effect at oil dispersion through formation of a rigid interfacial layer of biofilm. We show that the dispersion effectiveness of the commercial dispersant Corexit 9500A decreased approximately 25% in the presence of a mature microbial biofilm at the interface. Hexadecane biodegradation by the microbial culture was estimated, and it was found that approximately 90% of hexadecane was degraded in the period of 5 days. This work provides a comprehensive view on marine microbial biofilm from a detailed characterization at the formation stage to the overall role in the context of oil spill dispersion and further biodegradation. Bacterial biofilm and biosurfactants represent fully environmentally sustainable and natural materials for oil spill dispersion.