Coastal Marine Sediment Bacterial 16S rRNA Gene Sequencing

Photooxidation is an important fate process for crude oil in marine ecosystems, and resulting products are associated with their own environmental impacts. Oil and photolysis-derived products can be buried in marine sediments, where sulfate-reducing bacteria (SRB) play a key role in the biotransformation of these and other forms of organic carbon. Determining the impact of photolyzed oil-derived compounds on SRB is important with regard to predicting the impact of oil spills on carbon turnover in marine ecosystems. Sediments were collected from three Gulf of Mexico (GoM) locations. The impact of aqueous extracts of photolyzed Macondo source oil and individual polycyclic aromatic hydrocarbons (PAHs) on the respiratory activity of indigenous SRB communities was assessed via 35SO4-reduction activity (SRA) in sediment slurries amended with varying concentrations of photolyzed extracts (0.1 - 50%, v/v). Sediment microbial community composition, determined via 16S rRNA gene sequencing, revealed that sulfate-reducing, Ddeltaproteobacterial lineages were present and distinct at each location. Individual SRA experiments exhibited significant positive or negative responses in sulfate reduction rates (SRRs) in the presence of photooxidized hydrocarbons relative to baseline SRRs. However, no clear trends were observed for different sites, substrates, or irradiation treatments, suggesting that photolyzed oil is not likely has noto have an overall negative impact on sulfate-reducing microbial communities in coastal GoM sediments. More importantly, the oObserved increases in SRRs in some incubations suggest that indigenous microorganisms may play a role in the biotransformation of weathered hydrocarbon-derived contaminants in this ecosystem. As SRA is an integrated microbial community response, such findings suggest that photolyzed oil components are unlikely to significantly impact sediment sulfate-reducing microbial communities. Thus, toxicological assessments of photolyzed oil constituents should target other trophic levels.