Probing the bacteria-mediated agglomeration of dispersed oil

The effect of dispersant formulation on oil agglomeration and biodegradation was studied systematically using microscopy over a 15-day period by contacting a model oil (hexadecane) with an oil-degrading bacterium, Alcanivorax borkumensis, in the presence Corexit 9500 (CXT), a lecithin-Tween 80 mixture (LT), lecithin (L), and Tween 80 (T). CXT and LT successfully dispersed the oil, and bacteria adhered to and colonized the dispersed oil droplets, leading to the formation of agglomerates coated with bacterial biofilms. The size and structure of the agglomerates varied with the dispersant used. With CXT the agglomerates formed quickly, were large (> 100 µm), and contained live and dead bacteria. Comparatively, with LT the agglomerates formed slowly, were smaller (~ 50 µm), and contained primarily live bacteria. Despite these differences, the extent of oil biodegradation was similar in both cases. This study shows how agglomeration and biodegradation depends on a complex interplay between the actions of the dispersant and the bacteria.