研究团队在太平洋浮游植物 Citharistes regius 的共生系统中，发现一种超微小古菌「Candidatus Sukunaarchaeum mirabile」。其环状基因组只有 23.8 万个碱基对，远小于人类的数十亿与大肠杆菌的数百万，也不到先前最小古菌 Nanoarchaeum equitans（49 万个碱基对）的一半。

研究人员使用多种定序技术与组装程式交叉验证，确认这段极短序列是完整基因组而非分析假象。基因内容显示，Sukunaarchaeum 只保留了足以进行 DNA 复制与细胞分裂的最低限度蛋白质，几乎没有任何代谢相关基因，被迫将能量产生与生合成等功能完全外包给宿主细胞。

这种古菌被归入超小型的 DPANN 古菌类群，看来是一种几乎不回馈宿主的极端寄生者。相比之下，像 Carsonella ruddii 等细菌虽然基因组更小、约 15.9 万个碱基对，仍保留可供宿主胺基酸与维生素的代谢途径，却舍弃许多独立繁殖所需功能，显示在生命与类细胞寄生、乃至类胞器依赖之间存在多样演化路径。

Researchers studying seawater around the Pacific dinoflagellate Citharistes regius found an ultra-small archaeon, Candidatus Sukunaarchaeum mirabile, living in its symbiotic system. The circular genome is only 238,000 base pairs long, compared with several million in E. coli and billions in humans, and less than half the size of the previous archaeal record-holder Nanoarchaeum equitans at 490,000 base pairs.

The team verified the genome with multiple sequencing technologies and assembly programs, confirming that the tiny sequence is complete rather than an artifact. Gene-content analysis shows that Sukunaarchaeum encodes just enough proteins for DNA replication and cell division, but almost no genes for metabolism, forcing it to outsource energy production and biosynthesis entirely to a host cell.

Classified within the DPANN group of ultra-small archaea, Sukunaarchaeum appears to be an extreme parasite that provides little or no metabolic benefit to its partner. In contrast, bacteria such as Carsonella ruddii have even smaller genomes of about 159,000 base pairs but keep metabolic pathways that supply amino acids and vitamins, while shedding many functions needed for independent reproduction, underscoring diverse evolutionary routes toward quasi-life and organelle-like dependence.