Microorganisms that thrive along chemical and thermal gradients in deep-sea reducing environments, such as hydrothermal vents and cold seeps, colonize the interphase between the subseafloor environment and the ocean, effectively mediating the transfer of carbon and energy from the subsurface to the higher trophic levels. While chemoautotrophic microbial processes have been studied extensively in deep-sea reducing environments, we know less about heterotrophic microorganisms. In this project we are investigating aerobic hydrocarbon-oxidizing bacteria as a model system for heterotrophic processes in the deep-sea. These microorganisms oxidize subseafloor-generated hydrocarbons to fatty acids. The relevance of the proposed research to the C-DEBI themes lies in the contribution of hydrocarbonoclastic bacteria to the recycling of buried organic matter, effectively linking the subsurface environment to the ocean. Our experimental strategy includes the identification of genes and gene transcripts encoding for key enzymes in the oxidation of medium- and longchain n-alkanes. Results from this study provided a link between diversity and function in deep-sea aerobic hydrocarbonoclastic bacteria, resulted in the isolation of several heterotrophic deep-sea bacteria and revealed the reaction mechanisms of the metalloenzymes used by a selected subgroup of these hydrocarbon-oxidizing bacteria.