Department of Oceanography, Daniel K. Inouye Center for Microbial Oceanography: Research and Education (C-MORE), University of Hawai'i at Mānoa, Honolulu, HI, 96822, USA.
Department of Biological Sciences, California State University San Marcos, San Marcos, CA, 92096, USA.
Nat Commun. 2022 Feb 10;13(1):799. doi: 10.1038/s41467-022-28065-6.
Persistent nitrogen depletion in sunlit open ocean waters provides a favorable ecological niche for nitrogen-fixing (diazotrophic) cyanobacteria, some of which associate symbiotically with eukaryotic algae. All known marine examples of these symbioses have involved either centric diatom or haptophyte hosts. We report here the discovery and characterization of two distinct marine pennate diatom-diazotroph symbioses, which until now had only been observed in freshwater environments. Rhopalodiaceae diatoms Epithemia pelagica sp. nov. and Epithemia catenata sp. nov. were isolated repeatedly from the subtropical North Pacific Ocean, and analysis of sequence libraries reveals a global distribution. These symbioses likely escaped attention because the endosymbionts lack fluorescent photopigments, have nifH gene sequences similar to those of free-living unicellular cyanobacteria, and are lost in nitrogen-replete medium. Marine Rhopalodiaceae-diazotroph symbioses are a previously overlooked but widespread source of bioavailable nitrogen in marine habitats and provide new, easily cultured model organisms for the study of organelle evolution.
阳光充足的开阔海洋水中持续的氮消耗为固氮（固氮）蓝细菌提供了一个有利的生态位，其中一些与真核藻类共生。所有已知的这些共生的海洋例子都涉及到中心硅藻或甲藻宿主。我们在这里报告了两种不同的海洋舟形藻-固氮共生体的发现和特征，迄今为止，这些共生体仅在淡水环境中观察到过。从亚热带北太平洋中反复分离出新的浮游硅藻属海链藻属和链状海链藻属。序列文库的分析揭示了它们的全球分布。这些共生体可能逃脱了注意，因为内共生体缺乏荧光光色素，具有与自由生活的单细胞蓝细菌相似的 nifH 基因序列，并且在氮充足的培养基中丢失。海洋海链藻-固氮共生体是海洋生境中以前被忽视但广泛存在的生物可用氮源，为细胞器进化的研究提供了新的、易于培养的模式生物。
