Lamont-Doherty Earth Observatory, Biology and Paleo Environment, Columbia University, Palisades, NY, USA.
Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA.
ISME J. 2019 Jan;13(1):118-131. doi: 10.1038/s41396-018-0262-2. Epub 2018 Aug 16.
In the surface ocean, light fuels photosynthetic carbon fixation of phytoplankton, playing a critical role in ecosystem processes including carbon export to the deep sea. In oligotrophic oceans, diatom-diazotroph associations (DDAs) play a keystone role in ecosystem function because diazotrophs can provide otherwise scarce biologically available nitrogen to the diatom host, fueling growth and subsequent carbon sequestration. Despite their importance, relatively little is known about the nature of these associations in situ. Here we used metatranscriptomic sequencing of surface samples from the North Pacific Subtropical Gyre (NPSG) to reconstruct patterns of gene expression for the diazotrophic symbiont Richelia and we examined how these patterns were integrated with those of the diatom host over day-night transitions. Richelia exhibited significant diel signals for genes related to photosynthesis, N fixation, and resource acquisition, among other processes. N fixation genes were significantly co-expressed with host nitrogen uptake and metabolism, as well as potential genes involved in carbon transport, which may underpin the exchange of nitrogen and carbon within this association. Patterns of expression suggested cell division was integrated between the host and symbiont across the diel cycle. Collectively these data suggest that symbiont-host physiological ecology is strongly interconnected in the NPSG.
在海洋表面，光为浮游植物的光合作用提供能量，对包括碳向深海输出在内的生态系统过程起着至关重要的作用。在贫营养的海洋中，硅藻-固氮菌联合体（DDAs）在生态系统功能中起着关键作用，因为固氮菌可以为硅藻宿主提供否则稀缺的生物可利用氮，促进其生长和随后的碳封存。尽管它们很重要，但人们对这些联合体在现场的性质知之甚少。在这里，我们使用来自北太平洋亚热带回旋（NPSG）的表面样本的宏转录组测序来重建共生固氮体 Richelia 的基因表达模式，并研究了这些模式如何在昼夜过渡期间与硅藻宿主的模式相整合。Richelia 的光合作用、固氮和资源获取等相关基因表现出明显的昼夜信号。固氮基因与宿主氮吸收和代谢以及潜在的与碳运输相关的基因显著共表达，这可能为该联合体中的氮和碳交换提供支持。表达模式表明，宿主和共生体之间的细胞分裂在昼夜周期内是整合在一起的。总的来说，这些数据表明，NPSG 中的共生体-宿主生理生态学是紧密相互关联的。
