Metagenomic Analysis of the Microbial Degradation of Polar Oil Compounds

The polar components of crude oil are of significant interest due to their increased water-solubility and potential toxicity to marine biota. To examine the biodegradation of this important component of oil, mesocosm experiments composed of seawater bacterial consortia exposed to polar oil compounds dissolved in sterile seawater were constructed. In addition, two sets of controls were used: (1) a seawater bacterial consortia amended with succinic acid, which was used as a simple carbon source instead of oil and; (2) a seawater bacterial consortia with no carbon amendments. All mesocosms were supplemented with nutrients and kept in the dark at room temperature for 14 days. Samples were taken in triplicate on T=0, T=7 and T=14 days. Microbial community structure was analyzed using Illumina paired end sequencing of the 16S rRNA gene (V3/4 region). Differences in the bacterial assemblages in seawater mesocosms were observed between those exposed to oil-derived compounds, those exposed to succinate, and the control mesocosm with no carbon amendments. Seawater communities with no carbon amendments were comprised of a mixture of Proteobacteria (~45% of all sequence reads) and Bacteroidetes (~48%) whereas both the succinate and oil amended mesocosms became more enriched in Proteobacteria (80%-90%). Succinate amended mesocosms were composed of Delta-, Alpha- and Gammaproteobacteria (~35%, 40% and 33% respectively) in contrast to oil amended mesocosms, which were dominated by Gammaproteobacteria (~90%). Shotgun metagenomic sequencing of a subset of samples was performed to compare the metabolic processes present in the different mesocosms. Integration of the metagenomic data with chemical data obtained in parallel by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is ongoing. Overall, this study aims to provide new insight into the weathering and degradation of crude oil-derived polar compounds in the marine environment.