Synechococcus nitrogen gene loss in iron-limited ocean regions.
Synechococcus nitrogen gene loss in iron-limited ocean regions.
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DOI：
10.1038/s43705-023-00314-9
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发表时间：
2023-10-02
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影响因子：
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通讯作者：
Gifford, Scott
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文献类型：
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作者：
Sharpe, Garrett;Zhao, Liang;Meyer, Meredith G;Gong, Weida;Burns, Shannon M;Tagliabue, Allesandro;Buck, Kristen N;Santoro, Alyson E;Graff, Jason R;Marchetti, Adrian;Gifford, Scott
聚球藻是高纬度地区最丰富的蓝藻，估计占每年海洋净初级生产力的17%。尽管聚球菌具有生物地球化学的重要性，但海洋对岸的聚球菌种群采样并不均匀，大多数研究都集中在低纬度菌株上。特别是，在高纬度、高营养、低叶绿素(HNLC)地区几乎没有聚球藻基因组，这使得我们对微囊藻对铁限制的适应及其对碳、氮和铁循环的影响的了解出现了空白。我们用定量元基因组学研究了亚北极北太平洋的聚球藻种群，这是一个具有良好特征的HNLC地区。用短和长的读数组装产生了两个接近完整的聚球藻基因组(MAG)。这些种群来自元基因组的定量丰度与流式细胞仪计数很好地匹配，聚球藻估计占P站聚球菌的99%。而P站聚球菌含有多个适应铁限制的基因，两个基因组都缺乏吸收和同化硝酸盐和亚硝酸盐的基因，这表明对铵、尿素和其他形式的循环氮的依赖导致铁需求减少。对Tara Ocean数据集中聚球藻硝酸还原酶丰度的全球分析发现，其他HNLC地区的硝酸盐同化基因也较低。我们认为，聚球藻中硝酸盐和亚硝酸盐同化基因的丢失可能代表着对高纬度地区严重的铁限制的适应，那里的铵可利用性更高。我们的发现对量化蓝藻对初级生产和随后的碳输出的贡献的模型具有指导意义。
Synechococcus are the most abundant cyanobacteria in high latitude regions and are responsible for an estimated 17% of annual marine net primary productivity. Despite their biogeochemical importance, Synechococcus populations have been unevenly sampled across the ocean, with most studies focused on low-latitude strains. In particular, the near absence of Synechococcus genomes from high-latitude, High Nutrient Low Chlorophyll (HNLC) regions leaves a gap in our knowledge of picocyanobacterial adaptations to iron limitation and their influence on carbon, nitrogen, and iron cycles. We examined Synechococcus populations from the subarctic North Pacific, a well-characterized HNLC region, with quantitative metagenomics. Assembly with short and long reads produced two near complete Synechococcus metagenome-assembled genomes (MAGs). Quantitative metagenome-derived abundances of these populations matched well with flow cytometry counts, and the Synechococcus MAGs were estimated to comprise >99% of the Synechococcus at Station P. Whereas the Station P Synechococcus MAGs contained multiple genes for adaptation to iron limitation, both genomes lacked genes for uptake and assimilation of nitrate and nitrite, suggesting a dependence on ammonium, urea, and other forms of recycled nitrogen leading to reduced iron requirements. A global analysis of Synechococcus nitrate reductase abundance in the TARA Oceans dataset found nitrate assimilation genes are also lower in other HNLC regions. We propose that nitrate and nitrite assimilation gene loss in Synechococcus may represent an adaptation to severe iron limitation in high-latitude regions where ammonium availability is higher. Our findings have implications for models that quantify the contribution of cyanobacteria to primary production and subsequent carbon export.