S65: Ecology of hydrocarbon-degrading bacteria in Gulf of Mexico beach sands impacted by the Deepwater Horizon oil spill

Objectives of this research are to: 1) identify predominant oil-degrading taxa that may be employed as model hydrocarbon-degraders or as microbial indicators of contamination, and 2) characterize the in situ response of indigenous bacterial communities to oil contamination in beach ecosystems. Comparison of beach sands to the DH source oil indicate substantial weathering in that the majority of detectable hydrocarbon compounds that remained resided in the higher molecular weight aliphatic (>C16) and aromatic (>C35) fractions.  Twenty-four bacterial strains from 14 genera were isolated from oiled beach sands and confirmed as oil-degrading microorganisms by phenotypic characterization and phylogenetic analysis of 16S rRNA gene sequences. Isolated bacterial strains were primarily Gammaproteobacteria, including key genera of known oil-degraders. SSU rRNA sequences from oiled sands revealed phylotypes that showed high sequence identity to sequences from the oil-degrading bacterial isolates. SSU rRNA gene copy numbers of total bacteria were approximately 10 times higher in oiled (4.57 – 12.8 x 10⁷ copies g^-1) vs. clean (.0967 - .737 x 10⁷ copies g^-1) sand.  Community analysis indicated a strong response to oil contamination, and SSU rRNA gene sequences derived from genus Alcanivorax showed the largest increase in relative abundance in contaminated samples. Based on a combination of culture-based and cultivation-independent molecular approaches, we show that oil contamination from the DH spill has a profound impact on the abundance and community composition of indigenous bacteria in Gulf beach sands, and our evidence points to members of the Gammaproteobacteria and Alphaproteobacteria as key players in oil degradation there.