The field of molecular microbial ecology is entering a second age, going beyond simple surveys of diversity and revealing organized patterns of diversity consistent with ecological concepts that were once thought only applicable to ‘macro-scopic’ organisms. Recent discoveries of synchrony among independent microbial communities, taxa-area relationships, and bacterial endemism call for cohesive, large-scale studies of microbial diversity in systems hosting comparable microbial communities. Freshwater bacterioplankton are particularly useful for this purpose because of their relatively restricted diversity and their global distribution. These organisms are ecologically important, catalyzing critical biogeochemical reactions and serving as central members of aquatic microbial food webs. Diversity studies, conducted mainly in lakes, indicate bacterioplankton communities are dynamic, responding to spatial and temporal environmental gradients with shifts in dominant phylotypes. In rivers, such shifts can be rapid and extreme because of short water residence time. This sensitivity makes river bacterioplankton ideal for identifying environmental controls on the composition of microbial communities. Unfortunately, very little is known about the diversity and dynamics of river bacterioplankton. In fact, of the 25 largest rivers on the planet, only two have ribosomal DNA sequences entered in Genbank (Columbia R. and ChangJiang R.). Our first goal for this project is to test for hemisphere-scale patterns of bacterial diversity by characterizing and comparing the bacterioplankton diversity of the six largest rivers in the Arctic Ocean watershed, including five of the world’s largest rivers (Ob', Yenisey, Lena, Mackenzie, Yukon, and Kolyma rivers), and interpreting these patterns by relating them to an extensive complementary database of physical, chemical and biological measurements.

In collaboration with the PARTNERS group (Pan-Arctic River Transport of Nutrients, Organic Matter and Suspended Sediments; NSF-OPP-0229302), we are collecting high quality DNA samples from the mouths of these six rivers over a 4 years period beginning in 2003 (Partners Sampling Protocol) . The overall goal of the PARTNERS project is to use river water chemistry as a tool to study the origins and fates of continental runoff to the Arctic Ocean. Freshwater bacterioplankton may be useful as river-specific genetic tracers of freshwater in the Arctic Ocean as they are easily distinguishable from marine bacterioplankton using molecular techniques. Our second goal is to survey Arctic Rivers for abundant, persistent, river-specific bacterial phylotypes, design PCR primers targeting these organisms, and test whether these primers can detect highly dilute freshwater bacteria in the Arctic Ocean.