| Summary: | This research investigated the extent of nitrogen fixation and the structure of the diazotroph (N2-fixing) community in the coastal Alaskan Arctic. Samples to investigate the diazotroph community structure using the amplification of the nitriogenase gene (nifH) were collected during the summer of 2016 encompassing coastal regions in the Bering, Chukchi and Beaufort Seas with a specific interest in the areas of high productivity surrounding the Hanna Shoal region of the Chukchi Sea. Analysis of the diazotroph community led to the discovery that an unusual marine symbiosis involving two single celled partners – a eukaryotic (Haptophyte) algae and a unicellular cyanobacterial diazotroph (called UCYN-A) – was present in the Bering Sea. This remarkable symbiosis is broadly distributed throughout the world’s oceans, in both coastal and open ocean ecosystems but was not expected in the Arctic, and this is the first demonstration that it can fix nitrogen in cold water at rates similar to that in temperate and subtropical waters. This discovery opens many questions about the biology of this symbiosis, as well as its global role in fixing nitrogen. In addition to the UCYN-A symbiosis, we detected a diverse community of non-cyanobacterial diazotrophs, which are enigmatic, poorly understood groups encompassing many lineages of bacteria.
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