Starter Grant: Diversity and Activity of Denitrifiers Across Estuarine Gradients

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A grant has been awarded to Dr. Chris Francis of Stanford University to investigate how the distribution, diversity, and activity of denitrifying bacteria are influenced by environmental gradients in Elkhorn Slough, a small California estuary that opens into Monterey Bay. Denitrification, the transformation of nitrate and nitrite to gaseous products (NO, N2O, N2) under anaerobic conditions, is the main biological process responsible for returning fixed (usable) nitrogen from ecosystems to the atmosphere. Surprisingly, how environmental factors known to control denitrification rates (e.g., nitrate, organic carbon, oxygen, etc.) influence the diversity of denitrifying microbial communities is poorly understood. Elkhorn Slough, encompassing a wide range of physical/chemical gradients, is an ideal natural system in which to utilize both molecular biological (i.e., DNA-based) and cultivation approaches to address such questions. In particular, genes encoding nitrite reductase, the enzyme responsible for the key step of the denitrification pathway (NO2- - NO) will be used as a molecular marker to characterize the diversity of denitrifying bacteria in sediment samples collected at four sites along the estuary. In order to compile a culture collection of novel estuarine denitrifiers, for which virtually nothing is currently known, intensive cultivation studies will also be undertaken in the Slough. Elkhorn Slough is a principal wetland complex in central California and is considered one of the most ecologically important estuaries in the state, as evidenced by its rare National Estuarine Research Reserve (NERR) status. Roughly 25-50% of external nitrogen inputs are removed by denitrification in this treasured estuary, and this project will provide critical information regarding how the underlying microbial communities are influenced by complex environmental gradients. The resultant collections of nitrite reductase gene sequences and estuarine denitrifers will provide a valuable resource to the scientific community and, ultimately, reveal insights into the ecology and regulation of this biogeochemically-important process in all estuarine (and coastal) systems. Finally, this project will help support the research of graduate students.