The study investigates the biological effects and fate of the Deepwater Horizon oil spill in the Gulf of Mexico, focusing on the dispersed hydrocarbon plume. The research team collected deep-water samples from various distances from the wellhead and analyzed their physical, chemical, and microbiological properties. They found a significant increase in microbial cell densities and biomass in the plume, particularly in γ-Proteobacteria, which are known for their hydrocarbon-degrading capabilities. The plume was enriched with psychrophilic and psychrotolerant species, suggesting that these bacteria are adapted to low temperatures. Hydrocarbon-degrading genes were closely associated with the concentration of oil contaminants, indicating rapid biodegradation rates at 5°C. The study also used SR-FTIR spectroscopy to identify oil degradation products in the plume. Overall, the results suggest that intrinsic bioremediation of the oil plume is possible without substantial oxygen drawdown, highlighting the potential role of deep-sea microorganisms in controlling hydrocarbon fates in the Gulf.The study investigates the biological effects and fate of the Deepwater Horizon oil spill in the Gulf of Mexico, focusing on the dispersed hydrocarbon plume. The research team collected deep-water samples from various distances from the wellhead and analyzed their physical, chemical, and microbiological properties. They found a significant increase in microbial cell densities and biomass in the plume, particularly in γ-Proteobacteria, which are known for their hydrocarbon-degrading capabilities. The plume was enriched with psychrophilic and psychrotolerant species, suggesting that these bacteria are adapted to low temperatures. Hydrocarbon-degrading genes were closely associated with the concentration of oil contaminants, indicating rapid biodegradation rates at 5°C. The study also used SR-FTIR spectroscopy to identify oil degradation products in the plume. Overall, the results suggest that intrinsic bioremediation of the oil plume is possible without substantial oxygen drawdown, highlighting the potential role of deep-sea microorganisms in controlling hydrocarbon fates in the Gulf.