珪藻の窒素固定に根粒菌が関与している可能性が示唆される(Rhizobial bacterium helps diatom to bind nitrogen)

2024-05-09 マックス・プランク研究所

The Rhizobial nitrogen fixing symbionts (fluorescently-labeled in orange and green using genetic probes) residing inside diatoms collected from the tropical North Atlantic. The nucleus of the diatom is shown in bright blue.
© MPI f. Marine Microbiology/ Mertcan Esti

<関連情報>

• https://www.mpg.de/21885340/0429-mbio-new-rhizobia-diatom-symbiosis-solves-long-standing-marine-mystery-154772-x
• https://www.nature.com/articles/s41586-024-07495-w

根粒菌と珪藻の共生が海洋で不足する窒素を固定する Rhizobia–diatom symbiosis fixes missing nitrogen in the ocean

Bernhard Tschitschko,Mertcan Esti,Miriam Philippi,Abiel T. Kidane,Sten Littmann,Katharina Kitzinger,Daan R. Speth,Shengjie Li,Alexandra Kraberg,Daniela Tienken,Hannah K. Marchant,Boran Kartal,Jana Milucka,Wiebke Mohr & Marcel M. M. Kuypers
Nature  Published:09 May 2024
DOI:https://doi.org/10.1038/s41586-024-07495-w

We are providing an unedited version of this manuscript to give early access to its findings. Before final publication, the manuscript will undergo further editing. Please note there may be errors present which affect the content, and all legal disclaimers apply.

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 archaea^3-5. 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, and that they may be responsible for N₂ fixation in the vast regions of the ocean where cyanobacteria are too rare to account for the measured rates.