西班牙海洋科学研究所Francisco M. Cornejo-Castillo等研究人员合作发现，代谢权衡制约固氮共生中的细胞大小比例。2024年3月11日，《细胞》杂志在线发表了这项成果。

研究人员表示，生物固氮（N₂）是原核生物独有的关键代谢过程，其中一些原核生物与真核生物共生。海洋藻类Braarudosphaera bigelowii的一些物种包藏着固定N₂的内共生蓝藻UCYN-A，它们可能正在演化出类似细胞器的特征。

研究人员发现，UCYN-A及其宿主之间的大小比例在不同亚系/物种之间惊人地保持一致，这与该共生体及其他物种中细胞器的大小关系一致。代谢模型显示，这种大小关系使基于资源获取和交换之间权衡的协调增长率最大化。这些研究结果表明，单细胞真核生物中固定N₂的内共生体和细胞器的大小关系受到可预测的新陈代谢基础的制约，UCYN-A在许多方面的功能类似于潜在的N₂固定细胞器（或nitroplast）。

附：英文原文

Title: Metabolic trade-offs constrain the cell size ratio in a nitrogen-fixing symbiosis

Author: Francisco M. Cornejo-Castillo, Keisuke Inomura, Jonathan P. Zehr, Michael J. Follows

Issue&Volume: 2024-03-11

Abstract: Biological dinitrogen (N2) fixation is a key metabolic process exclusively performed by prokaryotes, some of which are symbiotic with eukaryotes. Species of the marine haptophyte algae Braarudosphaera bigelowii harbor the N2-fixing endosymbiotic cyanobacteria UCYN-A, which might be evolving organelle-like characteristics. We found that the size ratio between UCYN-A and their hosts is strikingly conserved across sublineages/species, which is consistent with the size relationships of organelles in this symbiosis and other species. Metabolic modeling showed that this size relationship maximizes the coordinated growth rate based on trade-offs between resource acquisition and exchange. Our findings show that the size relationships of N2-fixing endosymbionts and organelles in unicellular eukaryotes are constrained by predictable metabolic underpinnings and that UCYN-A is, in many regards, functioning like a hypothetical N2-fixing organelle (or nitroplast).

DOI: 10.1016/j.cell.2024.02.016

Source: https://www.cell.com/cell/fulltext/S0092-8674(24)00182-X