Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean
Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean
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DOI：
10.1128/aem.02137-17
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发表时间：
2018-02-01
影响因子：
4.4
通讯作者：
Hutchins, David A.
中科院分区：
文献类型：
--
作者：
Walworth, Nathan G.;Fu, Fei-Xue;Hutchins, David A.
固氮（N-2）蓝藻提供生物可利用的氮，以广大的海洋区域，但反过来限制铁（Fe）和/或磷（P），这可能迫使他们采用替代的氮获取策略。在营养有限的条件下，固氮菌对全球变化驱动因素的适应性反应可能会深刻改变目前海洋的氮和碳循环。在这里，我们表明，全球重要的N-2固定Trichodesmium从根本上改变氮代谢对有机氮清除以下长期高CO2适应铁和/或磷（CO）的限制。在高CO2/Fe限制和/或P限制条件下，转录物和蛋白质的全球变化包括N-2固定固氮酶的减少，加上氧化三甲胺（TMA）的酶的主要增加。TMA是一种丰富的、在生态化学上重要的有机氮化合物，其支持束毛藻的快速生长，同时抑制N-2固定。在未来的高CO2海洋中，这种全细胞能量重新分配，用于清除有机氮，而远离N-2固定，可能会减少束毛藻的新氮输入，同时耗尽氮有限的开放海洋生态系统中稀缺的固定氮供应。重要性束毛藻是海洋中最具生态化学意义的微生物之一，因为它提供了多达50%的新氮，支持开放海洋食物网。我们使用Trichodesmium文化适应高CO2条件7年，随后额外暴露于铁和/或磷（CO）限制。我们发现，“未来海洋”的高CO2和并发营养限制的条件下，从根本上改变氮代谢远离固氮，而不是对有机氮清除途径的上调。我们表明，预测未来的海洋条件的束丝藻的反应包括减少固氮酶加上酶的氧化丰富的有机氮源三甲胺（TMA）的主要增加。这种向有机氮吸收和远离固氮的转变可能会大大减少束毛藻向未来高CO2海洋中其他微生物群落的新氮输入，对海洋碳和氮循环具有潜在的全球影响。
Nitrogen-fixing (N-2) cyanobacteria provide bioavailable nitrogen to vast ocean regions but are in turn limited by iron (Fe) and/or phosphorus (P), which may force them to employ alternative nitrogen acquisition strategies. The adaptive responses of nitrogen fixers to global-change drivers under nutrient-limited conditions could profoundly alter the current ocean nitrogen and carbon cycles. Here, we show that the globally important N-2 fixer Trichodesmium fundamentally shifts nitrogen metabolism toward organic-nitrogen scavenging following long-term high-CO2 adaptation under iron and/or phosphorus (co) limitation. Global shifts in transcripts and proteins under high-CO2/Fe-limited and/or P-limited conditions include decreases in the N-2-fixing nitrogenase enzyme, coupled with major increases in enzymes that oxidize trimethylamine (TMA). TMA is an abundant, biogeochemically important organic nitrogen compound that supports rapid Trichodesmium growth while inhibiting N-2 fixation. In a future high-CO2 ocean, this whole-cell energetic reallocation toward organic nitrogen scavenging and away from N-2 fixation may reduce new-nitrogen inputs by Trichodesmium while simultaneously depleting the scarce fixed-nitrogen supplies of nitrogen-limited open-ocean ecosystems.IMPORTANCE Trichodesmium is among the most biogeochemically significant microorganisms in the ocean, since it supplies up to 50% of the new nitrogen supporting open-ocean food webs. We used Trichodesmium cultures adapted to high-CO2 conditions for 7 years, followed by additional exposure to iron and/or phosphorus (co) limitation. We show that " future ocean" conditions of high CO2 and concurrent nutrient limitation(s) fundamentally shift nitrogen metabolism away from nitrogen fixation and instead toward upregulation of organic nitrogen-scavenging pathways. We show that the responses of Trichodesmium to projected future ocean conditions include decreases in the nitrogen-fixing nitrogenase enzymes coupled with major increases in enzymes that oxidize the abundant organic nitrogen source trimethylamine (TMA). Such a shift toward organic nitrogen uptake and away from nitrogen fixation may substantially reduce new-nitrogen inputs by Trichodesmium to the rest of the microbial community in the future high-CO2 ocean, with potential global implications for ocean carbon and nitrogen cycling.