Occurrence and roles of the obligate hydrocarbonoclastic bacteria in the ocean when there is no obvious hydrocarbon contamination

The obligate hydrocarbonoclastic bacteria (OHCB) are an intriguing group of microorganisms for their unique ability to utilize hydrocarbons almost exclusively as a sole source of carbon and energy. Based on their narrow nutritional requirement for hydrocarbons as their major food source, these organisms are nonetheless found distributed throughout the global ocean and not confined to regions where there is an obvious source of petrochemical contamination from either anthropogenic (e.g., oil spills) or natural (e.g., oil seep) sources. The OHCB have been found in seawater and sediment samples collected from remote oligotrophic regions, such as Arctic and Antarctic waters, where there is no obvious hydrocarbon pollution. Some recently discovered OHCB have not yet been found in oil-contaminated sites. Collectively, this suggests that these organisms would likely be acquiring hydrocarbon or hydrocarbon-like substrates from sources other than the obvious oil spills and oil seeps. This chapter therefore provides a look at the various possible sources from which the OHCB could acquire hydrocarbons that may play an important part to sustaining their existence in remote and “pristine” marine environments.