Effects of the Deepwater Horizon oil spill on indigenous microbial communities in Pensacola Beach sands

Abstract

The destruction of the Deepwater Horizon (DH) oil rig discharged approximately 4.9 million barrels of light crude oil into marine environments from April 20, 2010 to July 15, 2010. A significant amount of oil washed ashore on beaches in the Gulf of Mexico and was subsequently buried underneath layers of sand. The overall goal of this project was to investigate the temporal effects of oil contamination from the DH spill on indigenous microbial communities in Pensacola Beach sands. Shifts in the community composition of bacteria and archaea were determined using high-throughput sequencing of 16S SSU rRNA genes, and gravimetric analysis was used to quantify oil degradation by known oil-degrading taxa enriched and isolated from oil contaminated beach sands in the Gulf of Mexico. Amplicon sequencing revealed significant decreases in microbial diversity as well as a shift in the microbial community to Gammaproteobacterial and Alphaproteobacterial lineages (~80% of the community) in oil contaminated sands. Many of the dominant operational taxonomic units (OTU) detected in abundance in oiled sands showed high sequence identity to known oil-degrading bacteria. Clean sands were dominated by different Gammaproteobacteria and members of the Thaumarchaeota. Archaea were more abundant in uncontaminated sands and are thought to be inhibited by oiling. A succession of microbial populations was observed from known aliphatic degraders to polycyclic aromatic hydrocarbon degraders as components of the oil were preferentially degraded. Isolates enriched from oil contaminated sands degraded significantly more oil than uninoculated control groups, illustrating that ecologically relevant bacteria abundant in oil contaminated communities are capable of oil degradation. Thus, we conclude that blooms of oil-degrading taxa are associated with the removal of hydrocarbons from the environment.