Meta-Omics Analysis Demonstrates the Weathering and Biodegradation of MC252 Oil in Sand Patties Originating from the Deepwater Horizon Oil Spill

Remnants of the Deepwater Horizon oil spill continue to wash ashore on Gulf of Mexico beaches as weathered sand patties (i.e., oil-sand aggregates). Little is known about the microbial ecology of these small oil systems and whether communities mediate hydrocarbon degradation following deposition. Sand patties were collected from Fort Morgan and Gulf Shores, Alabama, along with beach sand and seawater samples. GC x GC-FID was used for characterization and fingerprinting of oil extracted from the samples. Microbial community DNA from sand, seawater and sand patties was extracted for 16S rRNA gene amplicon and metagenomic Illumina sequencing. LC-Q/TOF high resolution mass spectrometry was used to survey for metabolites indicative of hydrocarbon degradation. GC x GC-FID analysis indicated that the sand patties contain highly weathered MC252 oil. Furthermore, the fraction of the oxygenated hydrocarbons, which are products of oil hydrocarbon degradation, contributed to more than 50% of the mass of sample extracts. Analysis of 16S gene sequences indicated that sand patty communities were distinct from those in sand and seawater. Metagenomic analysis revealed the genetic potential for aerobic and anaerobic hydrocarbon degradation via the detection of alkane hydroxylases, aromatic hydrocarbon oxygenases (e.g., benzene 1,2-dioxygenase, catechol 1,2-dioxygenase, and catechol 2,3-dioxygenase), and benzyl- and alkylsuccinate synthases. Hydrocarbon-derived metabolites consistent with aerobic and anaerobic processes were also identified in sand patties (e.g., toluate, benzoate, benzylsuccinates) indicating that degradation occurs in situ, whereas these metabolites were not observed in beach sand. Together, these data suggest the potential for the long-term attenuation and biodegradation of residual MC252 oil.