近日，德国马克斯·普朗克海洋微生物研究所Marcel M. M. Kuypers及其团队发现，根瘤菌-硅藻共生可固定海洋中缺失的氮元素。2024年5月9日，《自然》杂志在线发表了这项成果。

研究人员报告发现了一种非蓝藻固定氮（N₂）的共生体——Candidatus Tectiglobus diatomicola，它为硅藻宿主提供固定的氮（N），以换取光合碳。这种固定N₂的共生体属于根瘤菌纲，它与单细胞硅藻的结合扩大了根瘤菌纲的已知宿主范围，超越了众所周知的陆地上固定N₂的根瘤菌与豆科植物的共生关系。这些研究结果表明，在热带北大西洋，根瘤菌-硅藻共生对固定氮的贡献与蓝藻固定氮的贡献不相上下。

据悉，贫营养表层水域的N₂固定是海洋新N的主要来源，并在推动生物碳泵方面发挥着关键作用。尽管将N₂固定为氨的酶（氮酶的编码基因）在海洋细菌和古细菌中广泛存在，但海洋N₂固定几乎完全归功于蓝藻。人们对这些非蓝藻N₂固定者知之甚少，也缺乏它们能在海洋中固定氮的直接证据。

附：英文原文

Title: Rhizobia–diatom symbiosis fixes missing nitrogen in the ocean

Author: Tschitschko, Bernhard, Esti, Mertcan, Philippi, Miriam, Kidane, Abiel T., Littmann, Sten, Kitzinger, Katharina, Speth, Daan R., Li, Shengjie, Kraberg, Alexandra, Tienken, Daniela, Marchant, Hannah K., Kartal, Boran, Milucka, Jana, Mohr, Wiebke, Kuypers, Marcel M. M.

Issue&Volume: 2024-05-09

Abstract: Nitrogen (N2) fixation in oligotrophic surface waters is the main source of new nitrogen (N) to the ocean1 and plays a key role in fueling the biological carbon pump2. Oceanic N2 fixation is almost exclusively attributed to cyanobacteria, even though genes encoding nitrogenase, the enzyme fixing N2 into ammonia, are widespread among marine bacteria and archaea3-5. Little is known about these non-cyanobacterial N2-fixers and direct proof that they can fix N in the ocean is missing. Here we report the discovery of a non-cyanobacterial N2-fixing symbiont, Candidatus Tectiglobus diatomicola, which provides its diatom host with fixed-N in return for photosynthetic carbon. The N2-fixing symbiont belongs to the order Rhizobiales and its association with a unicellular diatom expands the known hosts for this order beyond the well-known N2-fixing rhizobia-legume symbioses on land6. Our results show that the rhizobia-diatom symbiosis can contribute as much fixed-N as cyanobacterial N2-fixers in the tropical North Atlantic.

DOI: 10.1038/s41586-024-07495-w

Source: https://www.nature.com/articles/s41586-024-07495-w