UCYN-A/haptophyte symbiosis presence revealed by sequencing nitriogenase gene (nifH) diversity in the Bering, Chukchi and Beaufort Seas, September 2016

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.

本研究针对阿拉斯加北极沿海区域的固氮作用强度及固氮微生物（diazotroph，N₂-fixing）群落结构开展调查。2016年夏季，研究团队于白令海、楚科奇海与波弗特海的沿海海域采集样本，通过扩增固氮酶基因（nifH）解析固氮微生物群落结构，重点关注楚科奇海汉娜浅滩周边的高生产力海域。对固氮微生物群落的分析显示，白令海存在一种特殊的海洋共生体系：由真核定鞭藻（Haptophyte）藻类与单细胞蓝细菌固氮微生物（命名为UCYN-A）组成的双单细胞伙伴共生体。该共生体在全球沿海与远洋生态系统中广泛分布，但此前未在北极区域被发现；本研究首次证实其可在冷水环境中以与温带、亚热带水域相近的速率完成固氮过程。这一发现为该共生体系的生物学特性及其全球固氮功能带来了诸多科学议题。除UCYN-A共生体系外，本研究还检测到一类多样的非蓝细菌固氮微生物群落，此类类群神秘且尚未被充分研究，涵盖多个细菌演化谱系。