Composition and distribution of diazotrophs in the Baltic Sea
Composition and distribution of diazotrophs in the Baltic Sea
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DOI：
10.1016/j.ecss.2023.108527
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发表时间：
2023-10
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通讯作者：
Ellen R. Salamon Slater;K. Turk-Kubo;Søren Hallstrøm;K. Kesy;P. Laas;Jonathan D. Magasin;J. Zehr;Matthias Labrenz;L. Riemann
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作者：
Ellen R. Salamon Slater;K. Turk-Kubo;Søren Hallstrøm;K. Kesy;P. Laas;Jonathan D. Magasin;J. Zehr;Matthias Labrenz;L. Riemann
波罗的海的氮（N2）固定率是世界上每单位面积最高的。然而，除了丝状异型囊形成蓝藻，有关固氮微生物（固氮菌）的组成和分布的知识是有限的。为了解决这个问题，我们调查了固氮酶基因（nifH）的组成和表达在沿海（离岸<10公里）和离岸（离岸>10公里）站，在表面（平均）。1.8 m）和深度（avg. 24 μ m）和自由生活（0.2-3.0 μm）和颗粒相关的大小部分（>3 μm）。令人惊讶的是，nifH基因隶属于伪蓝藻和非蓝藻固氮生物（NCD）占主导地位的组成，而丝状杂胞形成蓝藻占近80%的thenifH转录本。盐度的组成有轻微的影响，但Aphanizomenon和nodularihowed增加相对if H基因的表达，在低和高盐度，分别pseudanabaena仅占5%的thenif H转录本和nif H基因的表达由Atelocyanobacterium thalassa（亚系UCYN-A2）主要观察到在最咸的波罗的海西部。唯一值得注意的表达NCD（高达15%的nifH转录本在一个给定的站）与南海岸的上升流事件相吻合，主要是由aPseudomonas-likenifHynomata型，经常发现在波罗的海。非传染性疾病的相对丰度占主导地位的沿海站，可能是由沉积物再悬浮证明了较高的浊度和DOC水平和沉积物固氮生物在远洋区的恢复。这项研究揭示了在波罗的海固氮生物的组成和活动的异质性，并强调了未来的N2固定研究，包括沿海和近海波罗的海沃茨的需要。
Nitrogen (N2) fixation rates in the brackish Baltic Sea are among the highest per unit of area in the world. However, beyond the filamentous heterocyst-forming cyanobacteria, knowledge about the composition and distribution of N2-fixing microbes (diazotrophs) is limited. To address this, we investigated nitrogenase gene (nifH) composition and expression at coastal (<10 km offshore) and offshore (>10 km offshore) stations, at surface (avg. 1.8 m) and at depth (avg. 24 m) and in free-living (0.2–3.0 μm) and particle-associated size fractions (>3 μm). Surprisingly,nifHgenes affiliated withPseudanabaenaand non-cyanobacterial diazotrophs (NCDs) dominated the composition whereas filamentous heterocyst-forming cyanobacteria accounted for almost 80% of thenifHtranscripts. Salinity had a minor influence on the composition, butAphanizomenonandNodulariashowed increased relativenifHgene expression at low and higher salinity, respectively.Pseudanabaenaonly accounted for up to 5% of thenifHtranscripts andnifHgene expression byCandidatusAtelocyanobacterium thalassa (sublineage UCYN-A2) was mainly observed in the most saline western part of the Baltic. The only notable expression by NCDs (up to 15% ofnifHtranscripts at a given station) coincided with an upwelling event at the southern coast and was largely accounted for by aPseudomonas-likenifHphylotype, recurrently found in the Baltic Sea. NCD relative abundances were dominant in coastal stations, presumably driven by sediment resuspension as evidenced by higher turbidity and DOC levels and the recovery of sediment diazotrophs in the pelagic zone. This study reveals the heterogeneity of the composition and activity of diazotrophs in the Baltic Sea, and underscores the need for future N2fixation studies that include coastal and offshore Baltic waters.