Data_Sheet_1_Copepod-Associated Gammaproteobacteria Respire Nitrate in the Open Ocean Surface Layers.docx

Microbial dissimilatory nitrate reduction to nitrite, or nitrate respiration, was detected in association with copepods in the oxygenated water column of the North Atlantic subtropical waters. These unexpected rates correspond to up to 0.09 nmol N copepod−1 d−1 and demonstrate a previously unaccounted nitrogen transformation in the oceanic pelagic surface layers. Genes and transcripts for both the periplasmic and membrane associated dissimilatory nitrate reduction pathways (Nap and Nar, respectively) were detected. The napA genes and transcripts were closely related with sequences from several clades of Vibrio sp., while the closest relatives of the narG sequences were Pseudoalteromonas spp. and Alteromonas spp., many of them representing clades only distantly related to previously described cultivated bacteria. The discovered activity demonstrates a novel Gammaproteobacterial respiratory role in copepod association, presumably providing energy for these facultatively anaerobic bacteria, while supporting a reductive path of nitrogen in the oxygenated water column of the open ocean.

在北大西洋亚热带水域的溶氧水层中，与桡足类动物相关联的微生物反硝化硝酸盐还原作用，或称硝酸盐呼吸作用，已被检测到。这些出乎意料的速率高达0.09 nmol N 桡足类动物−1 d−1，并在海洋浮游表层展示了之前未被计算的氮素转化过程。检测到了周质和膜结合的反硝化硝酸盐还原途径（分别称为Nap和Nar）的基因和转录本。napA基因和转录本与来自数个 Vibrio sp. 系统发育群的序列密切相关，而narG序列的最近亲缘种为Pseudoalteromonas spp. 和 Alteromonas spp.，其中许多代表的是与之前描述的栽培细菌仅有间接关系的系群。所发现的活动展示了在桡足类动物关联中的新型伽马蛋白菌呼吸作用，可能为这些条件性厌氧细菌提供能量，同时支持开放海洋溶氧水柱中的氮素还原途径。