OLI Funded Grant: Making a Living in the Deep Sea: Enhanced Cycling of Dissolved Organic Carbon and Nitrogen by Marine Piezophiles


Grant Funded: 2005

Enormous amounts of carbon and essential nutrients (nitrogen and phosphorus) are sequestered in the ocean in dissolved organic matter.   In many areas of the ocean, particularly in nutrient limited regions or mid ocean gyres, > 95-98% of dissolved N and P are sequestered as organic nutrients.   The high concentrations of dissolved organic nutrients in N and P limited regions of the ocean are particularly enigmatic, in view of a large body of recent evidence that shows many marine plankton and bacteria are capable of metabolizing N and P containing organic compounds.

Dissolved organic matter concentrations decrease rapidly below the euphotic zone due to consumption by deep sea bacteria. However, when surface seawater is incubated for long periods of time (up to 2 years) in the laboratory, very little degradation of DOC is observed. As a result, we have been unable to study the bacteria that degrade most of the organic carbon in the ocean, or the metabolic pathways that return a large fraction of N and P to phytoplankton. If a large fraction of DOC is cycled so rapidly in the environment, why is DOC so recalcitrant in laboratory bottle experiments?  One variable that has not been studied experimentally is pressure. Recent research on the genetic apparatus of deep-sea bacteria (piezophiles) shows these microbes are particularly well suited to degrade the types of compounds found in DOC. With this in mind, we propose to conduct a suite of controlled experiments to study the degradation of DOC at high pressures. In our experiments, we will couple the degradation of DOC to gene expression in piezophilic bacteria. Our goal is to identify the microbes responsible for DOC degradation and to use the metabolic pathways employed by bacteria to better understand DOC composition and cycling.