A deep-sea oil plume from the Deepwater Horizon spill stimulated indigenous γ-Proteobacteria, which are closely related to known petroleum degraders. Hydrocarbon-degrading genes were found in the plume, and hydrocarbon biodegradation rates were faster than expected at 5°C. The plume likely contained dispersed MC252 oil, and microbial respiration and oxygen consumption were observed, indicating hydrocarbon catabolism. Extractable hydrocarbons ranged from undetectable to 9.21 μg/liter in plume samples, with volatile aromatic hydrocarbons significantly higher in the plume. The average temperature in the plume was 4.7°C, and the pressure was 1136 dB. The plume significantly altered microbial community composition and structure, with a dominance of γ-Proteobacteria, many of which are psychrophilic and psychrotolerant. PhyloChip analysis revealed that 951 distinct bacterial taxa were present in the plume, with 16 significantly enriched. These taxa are likely involved in hydrocarbon degradation. Cloning and sequencing revealed that the plume samples were dominated by the order Oceanospirillales, which are known hydrocarbon degraders. The plume also showed distinct phospholipid fatty acid profiles, indicating microbial adaptation to oil contamination. SR-FTIR analysis confirmed the presence of oil degradation products. Hydrocarbon-degrading genes were significantly enriched in the plume, and their expression correlated with oil contaminant concentrations. The bioremediation potential of the deep-sea plume was assessed, with degradation rates calculated based on alkane data. The half-lives of oil in the plume ranged from 1.2 to 6.1 days, indicating rapid degradation. The results suggest that intrinsic bioremediation could play a significant role in controlling the fate of hydrocarbons in the Gulf. The study highlights the importance of deep-sea microbial communities in oil degradation and their potential for bioremediation.A deep-sea oil plume from the Deepwater Horizon spill stimulated indigenous γ-Proteobacteria, which are closely related to known petroleum degraders. Hydrocarbon-degrading genes were found in the plume, and hydrocarbon biodegradation rates were faster than expected at 5°C. The plume likely contained dispersed MC252 oil, and microbial respiration and oxygen consumption were observed, indicating hydrocarbon catabolism. Extractable hydrocarbons ranged from undetectable to 9.21 μg/liter in plume samples, with volatile aromatic hydrocarbons significantly higher in the plume. The average temperature in the plume was 4.7°C, and the pressure was 1136 dB. The plume significantly altered microbial community composition and structure, with a dominance of γ-Proteobacteria, many of which are psychrophilic and psychrotolerant. PhyloChip analysis revealed that 951 distinct bacterial taxa were present in the plume, with 16 significantly enriched. These taxa are likely involved in hydrocarbon degradation. Cloning and sequencing revealed that the plume samples were dominated by the order Oceanospirillales, which are known hydrocarbon degraders. The plume also showed distinct phospholipid fatty acid profiles, indicating microbial adaptation to oil contamination. SR-FTIR analysis confirmed the presence of oil degradation products. Hydrocarbon-degrading genes were significantly enriched in the plume, and their expression correlated with oil contaminant concentrations. The bioremediation potential of the deep-sea plume was assessed, with degradation rates calculated based on alkane data. The half-lives of oil in the plume ranged from 1.2 to 6.1 days, indicating rapid degradation. The results suggest that intrinsic bioremediation could play a significant role in controlling the fate of hydrocarbons in the Gulf. The study highlights the importance of deep-sea microbial communities in oil degradation and their potential for bioremediation.