Rhizobia-diatom symbiosis fixes missing nitrogen in the ocean

• 成果类型: Article
• 署名作者: 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.
• 署名单位: Max Planck Society; University of Vienna; Helmholtz Association; Alfred Wegener Institute, Helmholtz Centre for Polar & Marine Research; University of Bremen; Constructor University; University of Innsbruck
• 刊物名称: Nature
• ISSN/ISSBN: 0028-5055
• DOI: 10.1038/s41586-024-07495-w
• 发表日期: 2024-06-27
• 关键词: multiple sequence alignment; Fixation; database; pacific; fish; LIFE; tool

摘要

Nitrogen (N2) fixation in oligotrophic surface waters is the main source of new nitrogen to the ocean 1 and has a key role in fuelling the biological carbon pump 2 . Oceanic N2 fixation has been attributed almost exclusively to cyanobacteria, even though genes encoding nitrogenase, the enzyme that fixes N2 into ammonia, are widespread among marine bacteria and archaea 3-5 . Little is known about these non-cyanobacterial N2 fixers, and direct proof that they can fix nitrogen in the ocean has so far been lacking. Here we report the discovery of a non-cyanobacterial N2-fixing symbiont, 'Candidatus Tectiglobus diatomicola', which provides its diatom host with fixed nitrogen 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 land 6 . Our results show that the rhizobia-diatom symbioses can contribute as much fixed nitrogen as can cyanobacterial N2 fixers in the tropical North Atlantic, and that they might be responsible for N2 fixation in the vast regions of the ocean in which cyanobacteria are too rare to account for the measured rates. A symbiosis between a diatom and a newly discovered species of alphaproteobacteria, 'Candidatus Tectiglobus diatomicola', can fix nitrogen in the ocean, providing evidence that nitrogen fixers other than cyanobacteria have a key role in the marine environment.