Unusual marine cyanobacteria/haptophyte symbiosis relies on N2fixation even in N-rich environments
Unusual marine cyanobacteria/haptophyte symbiosis relies on N2fixation even in N-rich environments
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DOI：
10.1038/s41396-020-0691-6
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发表时间：
2020-06-10
期刊：
影响因子：
11
通讯作者：
Zehr, Jonathan P.
中科院分区：
文献类型：
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作者：
Mills, Matthew M.;Turk-Kubo, Kendra A.;Zehr, Jonathan P.
微生物对N（2）的固定是海洋生物可利用氮（N）的最大来源。然而，它是能量最昂贵的N-获取过程，并且当能量较低的形式，如溶解的无机N（DIN）可用时，被认为受到抑制。奇怪的是，世界性的N-2固定UCYN-A/附着菌共生体生长在DIN丰富的沃茨，但他们的N（2）固定DIN的敏感性是未知的。我们使用稳定同位素孵育，催化报告沉积荧光原位杂交（CARD-FISH），和纳米级二次离子质谱（nanoSIMS），调查的N源所使用的附着宿主和敏感性UCYN-A N（2）固定在DIN充满沃茨。我们表明，在我们的实验条件下，两个UCYN-A亚系的附着宿主不同化硝酸盐（NO3-），并通过铵（NH 4+）吸收满足他们的N需求很少。相反，UCYN-A/附着菌共生依赖于UCYN-A N（2）固定来提供附着菌的大部分N需求，即使在DIN充足的条件下。此外，UCYN-A的N（2）固定率，和附着植物宿主的碳固定率，在N-有限的沃茨中，有时被NO（3）（-）的增加所刺激，这表明大量的浮游植物组合的活动和UCYN-A/附着植物共生之间的联系。研究结果表明，即使在富含氮的沿海或高纬度沃茨，固氮生物-真核生物共生体的固氮固定可能是一种进化上可行的策略。
The microbial fixation of N(2)is the largest source of biologically available nitrogen (N) to the oceans. However, it is the most energetically expensive N-acquisition process and is believed inhibited when less energetically expensive forms, like dissolved inorganic N (DIN), are available. Curiously, the cosmopolitan N-2-fixing UCYN-A/haptophyte symbiosis grows in DIN-replete waters, but the sensitivity of their N(2)fixation to DIN is unknown. We used stable isotope incubations, catalyzed reporter deposition fluorescence in-situ hybridization (CARD-FISH), and nanoscale secondary ion mass spectrometry (nanoSIMS), to investigate the N source used by the haptophyte host and sensitivity of UCYN-A N(2)fixation in DIN-replete waters. We demonstrate that under our experimental conditions, the haptophyte hosts of two UCYN-A sublineages do not assimilate nitrate (NO3-) and meet little of their N demands via ammonium (NH4+) uptake. Instead the UCYN-A/haptophyte symbiosis relies on UCYN-A N(2)fixation to supply large portions of the haptophyte's N requirements, even under DIN-replete conditions. Furthermore, UCYN-A N(2)fixation rates, and haptophyte host carbon fixation rates, were at times stimulated by NO(3)(-)additions in N-limited waters suggesting a link between the activities of the bulk phytoplankton assemblage and the UCYN-A/haptophyte symbiosis. The results suggest N(2)fixation may be an evolutionarily viable strategy for diazotroph-eukaryote symbioses, even in N-rich coastal or high latitude waters.