Enhanced protein and carbohydrate hydrolyses in plume-associated deepwaters initially sampled during the early stages of the Deepwater Horizon oil spill

Oil spilled in the ocean can be biodegraded through a cascade of microbial processes, including direct degradation of petroleum-derived hydrocarbons, as well as subsequent degradation of transformation byproducts and exopolymeric substances (EPS) that are produced by microbes to emulsify hydrocarbons and facilitate access to oil. In the aftermath of the Deepwater Horizon oil spill, we measured enzymatic hydrolysis of carbohydrates and peptides in waters initially collected from within and outside of the deep hydrocarbon plume. The rationale is that the presence of EPS and other transformation byproducts in the deepwater plume may have enhanced heterotrophic bacterial metabolism in the cold deepwater environment. Our investigation targets carbohydrate and peptide hydrolase activities as indicators of the degradation of high molecular weight organic matter, including EPS substrates. Deepwater associated with the hydrocarbon plume revealed higher peptidase activity compared to non-plume deepwater samples. Enzymatic hydrolysis of carbohydrates, measured by the means of exo-acting enzyme activity (β-glucosidase), was also more rapid inside compared to outside the deepwater plume. Hydrolysis rates and patterns of endo-acting polysaccharide hydrolases, measured by means of distinct polysaccharide substrates in longer-term incubations, demonstrated more rapid plume-associated hydrolysis of two (laminarin and xylan) of the three substrates hydrolyzed in deepwaters. Our results indicate that microbial communities associated with the deepwater plume exhibited 'primed' responses to addition of specific substrates, which may structurally resemble components found in bacterial EPS and oil degradation byproducts. Bacterial transformation of oil-degradation byproducts thus likely contributed to microbial growth and respiration measured inside the deepwater plume.