The interplay between the marine diazotroph

Marine environments are frequently oligotrophic, characterized by low amount of bioassimilable nitrogen sources. At the global scale, the microbial fixation of N₂, or diazotrophy, represents the primary source of fixed nitrogen in pelagic marine ecosystems, playing a key role in supporting primary production and driving the export of organic matter to the deep ocean. However, given the high energetic cost of N₂ fixation, the active release of fixed nitrogen by diazotrophs appears counterintuitive, suggesting the existence of alternative passive release pathways that remain understudied to date. Here, we show that the marine non-cyanobacterial diazotroph IMPORTANCE: Diazotrophs are key players in ocean functioning by providing fixed nitrogen to ecosystems and fueling primary production. However, from a physiological point of view, the active release of nitrogenous compounds by diazotrophs is paradoxical, since they would invest in an energy-intensive process and supply nutrient to non-sibling cells, with the risk of being outcompeted. Therefore, alternative ways leading to the release of fixed nitrogen must exist. Here, we show that the marine non-cyanobacterial diazotroph