Probing the Chemical Transformation of Seawater-Soluble Crude Oil Components during Microbial Oxidation

Studies assessing the environmental impacts of oil spills focus primarily on the nonwater-soluble components, leaving the fate of the water-soluble fraction (WSF) largely unexplored. We employed untargeted chemical analysis along with biological information to probe the transformation of crude oil WSF in seawater in the absence of light in a laboratory experiment. Over a 14-day incubation, microbes transformed WSF into various metabolic intermediates without significantly altering the dissolved organic carbon concentrations. Microbial transformation processes increased the chemical diversity and overall oxygen content of WSF compounds, concomitant with an increase in dioxygenase gene abundances. While the majority of metabolites formed from the transformation of WSF could not be structurally identified with existing databases, elemental formulas suggest that many of these compounds could be oxidation products of water-soluble nonpolar compounds such as PAHs. In particular, metabolites with three oxygen atoms may represent a key transition point for WSF degradation. One such compound, salicylic acid, likely provides a route for complete WSF remineralization, as it is labile to marine bacteria. The environmental persistence and toxicity of WSF metabolic products are still unknown, but results from this study provide a framework for further exploration of the fate of WSF in marine ecosystems.