The effects of sunlight on the composition of exopolymeric substances affecting the subsequent aggregation process during oil spill and Corexit exposure

To test the effects of sunlight on the composition and secretion of exopolymeric substances (EPS) and the subsequent aggregation process, we conducted short-term irradiation experiments in three treatments, i.e., control (coastal seawater of the Gulf of Mexico), water accommodated fraction of oil (WAF), and chemically-enhanced WAF (CEWAF). EPS composition (mainly carbohydrates and proteins) were quantified in the colloidal fractions, and aggregates. In addition, bacterial abundance, live/dead cell ratio, and ambient •OH formation rate were measured under these conditions. In the presence of oil, natural sunlight stimulated polysaccharide secretion, partially due to increased ROS (i.e. •OH) production in the presence of oil. In addition, flow cytometry showed formation of larger sized aggregates in the irradiated WAF treatment, and polysaccharides accumulated into aggregates.