High cyanobacterial nif H gene diversity in Arctic seawater and sea ice brine

• Published in: Environmental Microbiology Reports
• Main Authors: Díez, Beatriz, Bergman, Birgitta, Pedrós‐Alió, Carlos, Antó, Meritxell, Snoeijs, Pauline
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Fram Strait; Greenland; Greenland Sea; Sea ice
• Online Access: http://dx.doi.org/10.1111/j.1758-2229.2012.00343.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1758-2229.2012.00343.x; http://onlinelibrary.wiley.com/wol1/doi/10.1111/j.1758-2229.2012.00343.x/fullpdf

Summary Although cyanobacterial diazotrophs are common in Arctic terrestrial and freshwater habitats, they have been assumed to be absent from Arctic marine habitats. We report here a high diversity of cyanobacterial nif H genes in Fram Strait and the Greenland Sea. The nif H gene encodes the iron protein of the nitrogenase enzyme complex, which is essential for biological N 2 fixation. Using primers specific for nif H genes we uncovered communities of autotrophic and heterotrophic bacteria in sea ice brine and seawater between latitudes 65 and 81°N. Cyanobacteria ( Oscillatoriales and Chroococcales ) with known marine planktonic and benthic distributions were distinguished, alongside a mix of metabolically versatile eubacteria ( nif H Clusters I and III). Using primers selective for cyanobacterial nif H genes we identified filamentous non‐heterocystous Trichodesmium ‐like and LPP ( Leptolyngbya, Phormidium and Plectonema )‐like Oscillatoriales , as well as Cyanothece ‐like Chroococcales in a brine sample from 81°N. The occurrence of Trichodesmium ‐like cyanobacteria was further confirmed by sequences of the het R gene of Trichodesmium . Microscopic examinations confirmed the presence of viable filamentous and unicellular cyanobacteria. Our results reveal the potential for microbial N 2 fixation in the Arctic seas. However, it is still left to determine if these genes are also metabolically active before any biogeochemical importance of diazotrophy in the polar oceans can be assessed.