Nitrate uptake by heterotrophic bacteria plays an important role in marine N cycling. However, few studies have investigated the diversity of environmental nitrate assimilating bacteria (NAB). In this study, the diversity and biogeographical distribution of NAB in several global oceans and particularly in the western Pacific marginal seas were investigated using both cultivation and culture-independent molecular approaches. Phylogenetic analyses based on 16S rRNA and nasA (encoding the large subunit of the assimilatory nitrate reductase) gene sequences indicated that the cultivable NAB in South China Sea belonged to the α-Proteobacteria, γ-Proteobacteria and CFB (Cytophaga-Flavobacteria-Bacteroides) bacterial groups. In all the environmental samples of the present study, α-Proteobacteria, γ-Proteobacteria and Bacteroidetes were found to be the dominant nasA-harboring bacteria. Almost all of the α-Proteobacteria OTUs were classified into three Roseobacter-like groups (I to III). Clone library analysis revealed previously underestimated nasA diversity; e.g. the nasA gene sequences affiliated with β-Proteobacteria, ε-Proteobacteria and Lentisphaerae were observed in the field investigation for the first time, to the best of our knowledge. The geographical and vertical distributions of seawater nasA-harboring bacteria indicated that NAB were highly diverse and ubiquitously distributed in the studied marginal seas and world oceans. Niche adaptation and separation and/or limited dispersal might mediate the NAB composition and community structure in different water bodies. In the shallow-water Kueishantao hydrothermal vent environment, chemolithoautotrophic sulfur-oxidizing bacteria were the primary NAB, indicating a unique nitrate-assimilating community in this extreme environment. In the coastal water of the East China Sea, the relative abundance of Alteromonas and Roseobacter-like nasA gene sequences responded closely to algal blooms, indicating that NAB may be active participants contributing to the bloom dynamics. Our statistical results suggested that salinity, temperature and nitrate may be some of the key environmental factors controlling the composition and dynamics of the marine NAB communities.

中文翻译：

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异养细菌 nasA 基因在不同海洋环境中的普遍性和多样性。

异养细菌对硝酸盐的吸收在海洋氮循环中起着重要作用。然而，很少有研究调查环境硝酸盐同化细菌（NAB）的多样性。在这项研究中，使用培养和独立于培养的分子方法研究了全球几个海洋，特别是西太平洋边缘海中 NAB 的多样性和生物地理分布。基于16S rRNA和nasA（编码同化硝酸盐还原酶大亚基）基因序列的系统发育分析表明，南海可培养的NAB属于α-变形菌门、γ-变形菌门和CFB（噬细胞菌-黄细菌-拟杆菌）细菌组。在本研究的所有环境样本中，α-变形菌门、γ-变形菌门和拟杆菌门被发现是主要的 nasA 携带细菌。几乎所有的 α-变形菌门 OTU 都被分为三个类玫瑰杆菌组（I 至 III）。克隆文库分析揭示了之前低估的 nasA 多样性；例如，据我们所知，属于β-变形菌门、ε-变形菌门和慢球菌门的nasA基因序列首次在实地调查中观察到。海水中携带 nasA 的细菌的地理和垂直分布表明，NAB 高度多样化，并且普遍分布在所研究的边缘海和世界海洋中。生态位适应和分离和/或有限的扩散可能调节不同水体中的 NAB 组成和群落结构。在浅水龟山岛热液喷口环境中，化能自养硫氧化细菌是主要的NAB，表明该极端环境中存在独特的硝酸盐同化群落。在东海沿岸水域，交替单胞菌和玫瑰杆菌样nasA基因序列的相对丰度与藻华密切相关，表明NAB可能是藻华动态的积极参与者。我们的统计结果表明，盐度、温度和硝酸盐可能是控制海洋 NAB 群落组成和动态的一些关键环境因素。