(192s) Microscopic Evolution of Biofilm Formation in Dispersed Oil Droplet-Bacteria Agglomerates

Oil degrading bacteria adhere to and colonize dispersed oil droplets, leading to biofilm formation in the form of free-floating agglomerates with entrapped oil droplets. Using a range of microscopy techniques, we have observed that the size and apparent density of biofilm agglomerates is dependent upon droplet size, which is in turn dependent upon dispersant composition. Biodegradation experiments were conducted in nutrient supplemented artificial seawater with Alcanivorax borkumensis utilizing hexadecane (a model oil) dispersed by Corexit 9500, a lecithin/Tween 80 mixture, and lecithin and Tween 80. Low initial bacteria and oil concentrations were used to allow direct imaging of the formation, size, and structure of the biofilm agglomerates as the systems evolved. With Corexit 9500, a mixture of non-ionic and anionic surfactants that formed small hexadecane droplets, the agglomerates formed quickly (within 1 day), were large and dense, and persisted for weeks. Comparatively, with lecithin/Tween 80, a mixture of a zwitterionic and a non-ionic surfactant that formed large droplets, the agglomerates took longer to form (2-3 days), were smaller and less-dense, and continued to grow over the course of the study. Lecithin nor Tween 80 alone led to the formation of biofilm agglomerates. Despite the distinct differences in the physical properties observed for the biofilm agglomerates, the extent of hexadecane biodegradation after two weeks was similar and ranged from approximately 30-50% for all dispersants examined. Lecithin/Tween 80 yielded the highest biodegradation possibly due to the surfactants being used as a nutrient or food source. While the size and structure of the biofilm agglomerates did not correlate with the extent of biodegradation, these properties did impact the colloidal properties of the agglomerates and their ability to sediment or cream.