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.