Québec-Océan, Université Laval, Québec, Quebec, Canada.
Département de Biologie, Université Laval, Québec, Quebec, Canada.
Appl Environ Microbiol. 2019 Jul 1;85(14). doi: 10.1128/AEM.00247-19. Print 2019 Jul 15.
For photosynthetic microbial eukaryotes, the rate-limiting step in NO assimilation is its reduction to nitrite (NO), which is catalyzed by assimilatory nitrate reductase (NR). Oceanic productivity is primarily limited by available nitrogen and, although nitrate is the most abundant form of available nitrogen in oceanic waters, little is known about the identity of microbial eukaryotes that take up nitrate. This lack of knowledge is especially severe for ice-covered seas that are being profoundly affected by climate change. To address this, we examined the distribution and diversity of NR genes in the Arctic region by way of clone libraries and data mining of available metagenomes (total of 4.24 billion reads). We directly compared NR clone phylogenies with the V4 region of the 18S rRNA gene (DNA pool) and 18S rRNA (RNA pool) at two ice-influenced stations in the Canada Basin (Beaufort Sea). The communities from the two nucleic acid templates were similar at the level of major groups, and species identified by way of NR gene phylogeny and microscopy were a subset of the 18S results. Most NR genes from arctic clone libraries matched diatoms and chromist nanoflagellates, including novel clades, while the NR genes in arctic eukaryote metagenomes were dominated by chlorophyte NR, in keeping with the ubiquitous occurrence of Mamiellophyceae in the Arctic Ocean. Overall, these data suggest that a dynamic and mixed eukaryotic community utilizes nitrate across the Arctic region, and they show the potential utility of NR as a tool to identify ongoing changes in arctic photosynthetic communities. To better understand the diversity of primary producers in the Arctic Ocean, we targeted a nitrogen cycle gene, NR, which is required for phytoplankton to assimilate nitrate into organic forms of nitrogen macromolecules. We compared this to the more detailed taxonomy from ice-influenced stations using a general taxonomic gene (18S rRNA). NR genes were ubiquitous and could be classified as belonging to diatoms, dinoflagellates, other flagellates, chlorophytes, and unknown microbial eukaryotes, suggesting novel diversity of both species and metabolism in arctic phytoplankton.
对于光合微生物真核生物，氮同化的限速步骤是将其还原为亚硝酸盐（NO），这是由同化硝酸盐还原酶（NR）催化的。海洋生产力主要受到可用氮的限制，尽管硝酸盐是海洋水中最丰富的可用氮形式，但对于吸收硝酸盐的微生物真核生物的身份知之甚少。这种知识的缺乏对于受气候变化深刻影响的冰雪覆盖的海洋来说尤为严重。为了解决这个问题，我们通过克隆文库和对可用宏基因组（总计 42.4 亿个读取）的数据挖掘，研究了北极地区 NR 基因的分布和多样性。我们直接将 NR 克隆系统发育与加拿大盆地（波弗特海）两个受冰影响的站点的 18S rRNA 基因的 V4 区（DNA 池）和 18S rRNA（RNA 池）进行比较。两个核酸模板的群落在主要类群水平上相似，通过 NR 基因系统发育和显微镜鉴定的物种是 18S 结果的一个子集。来自北极克隆文库的大多数 NR 基因与硅藻和 Chromista 纳米鞭毛藻相匹配，包括新的进化枝，而北极真核生物宏基因组中的 NR 基因主要由绿藻 NR 主导，这与 Mamiellophyceae 在北极海洋中的普遍存在相一致。总的来说，这些数据表明，一个动态和混合的真核生物群落在整个北极地区利用硝酸盐，并且它们显示了 NR 作为识别北极光合群落正在发生变化的工具的潜在用途。为了更好地了解北极海洋中初级生产者的多样性，我们针对氮循环基因 NR，NR 是浮游植物将硝酸盐同化到有机氮大分子中的必需基因。我们将其与受冰影响的站点的更详细分类群（18S rRNA）进行了比较。NR 基因无处不在，可以归类为硅藻、甲藻、其他鞭毛藻、绿藻和未知的微生物真核生物，这表明北极浮游植物的物种和代谢具有新的多样性。
