Protist Stimulation of Biodegradation of Hydrocarbons by In-situ Deep Sea Bacterial Communities


Co-funded ORI and DOEI Research: 2010


Recent events in the Gulf of Mexico have reignited interest in understanding the long-term consequences of contamination on the marine food web.  Unfortunately, not enough is known about the long-term process of biodegradation of hydrocarbons, particularly in deep-sea sediments.  Without this knowledge it is impossible to model the long-term consequences of a major spill on the marine environment.  Protists are unicellular eukaryotes that are an essential component of microbial food webs, and play key roles in global biogeochemical cycles.  Despite their ecological importance in aquatic and terrestrial ecosystems, relatively little is known about their role in hydrocarbon degradation compared with that reported for bacteria.  This is unsatisfying because the wide range of toxic effects that can result from hydrocarbon exposure including cancer, hepatotoxicity and porphyria in both humans and animals is well known, and many hydrocarbons are bioaccumulative.  As protists are preyed upon by zooplankton, benthic and pelagic filter feeders and fishes, they act as important vectors in transporting hydrocarbons to higher trophic levels.  A more detailed knowledge of the role of protists in microbial interactions with hydrocarbons is essential before we can trace and model the fate of hydrocarbon contaminants in terrestrial and aquatic ecosystems.  It is also now believed that hydrocarbon degradation is a multi-step procedure where each step is performed via distinct processes carried out by different functional groups of microbial organisms.  The few studies that addressed the subject to date indicate that protists play a significant role in the microbial ecology of contaminant degradation.  This project aims to determine if the presence of protists enhances the degradation of hydrocarbons in deep marine sediments under oxic and anoxic conditions and under varying nutrient (P and N) concentrations, what the impact of hydrocarbon contamination is on benthic microbial communities, and in particular, whether their presence leads to a restructuring of the in situ bacterial community.  For this pilot study deep sea sediments and seawater are on hand from 1) a naturally petroleum- and methane-rich site at 2000m depth in the Guaymas Basin, CA, and 2) deep Gulf of Mexico sediments from normal, non-seep benthic sediments from ca. 1000 m depth.