The Deepwater Horizon Disaster
Sunlight illuminating the lingering oil slick off the Mississippi Delta on May 24, 2010. (Wikimedia Commons)
Impacts of the Deepwater Horizon Oil Spill
Oyster Project: Gulf of Mexico oysters are prized for their economic value. Not only are oysters a valuable commodity as seafood; but oyster reefs provide a variety of ecosystem services including critical habitats for commercial fisheries, water filtration, and removal of excess nutrients from estuarine environments. The value of this habitat, however, can be greatly reduced by toxic oil discharges, such as those from the 2010 Deepwater Horizon oil (DWH) spill blowout. Effective response to such large-scale contamination of the marine environments requires a rapid and precise assessment of disturbances caused to the ecosystem such that timely mitigation strategies can be implemented. In this regard, biodegradative bacteria, as those identified from this and previous studies can significantly contribute to degradation of oil contaminants and rehabilitation of the perturbed environments. For example, stimulation of biodegradative communities within an impacted oyster reef ecosystem might be a potential remediation strategy to enhance cleanup and restoration efforts. However, baseline analyses of the oyster microbiome, which remains largely under-studied, are needed to develop successful approaches to problems of contamination of oyster reefs by petroleum and other hydrocarbons.
In this project, we evaluated the potential response of the Eastern oyster’s microbiome to hydrocarbon contamination and compares it with the bacterial community responses observed from the overlaying water column and the oyster bed sediments. For this purpose, microcosms seeded with DWH crude oil were established and inoculated separately with oyster tissue (OT), mantle fluid (MF), overlaying water column (WC) and sediments (S) collected from Apalachicola Bay, FL. Shifts in the microbial community structure in the amended microcosms was monitored over a 3-month period using automated ribosomal intergenic spacer region analysis (ARISA), which showed that the microbiome of the oyster tissue and mantle fluid were more similar to the sediment communities than those present in the overlaying water column. This pattern remained largely consistent, regardless of the concentration of crude oil or the enrichment period. Additionally, 72 oil-degrading bacteria were isolated from the microcosms containing OT, MF, WC and S and identified using 16S ribosomal RNA (rRNA) gene sequencing and compared by principal component analysis (PCA) which clearly showed that the water column isolates were different to those identified from the sediment. Conversely, the oyster tissue and mantle fluid isolates clustered together; a strong indication that the oyster microbiome is uniquely structured relative to its surrounding environment. When selected isolates from the OT, MF, WC and S were assessed for their oil-degrading potential, we found that the DWH oil was biodegraded between 12%-42%, under the existing conditions.
Oyster Metagenomes: Bacteria associated with the Eastern oysters (Crassostrea virginica) native to Apalachicola Bay, FL, were investigated using 16S rRNA gene amplicon metagenomic sequencing which revealed that the oyster microbiome was predominated by Cyanobacteria and Proteobacteria. We also found that the oyster tissues were predominated by the pathogenic and symbiotic Photobacterium spp. (formerly known as Vibrio damselae).