CTP synthase (CTPS) is an important metabolic enzyme that catalyzes the rate-limiting reaction of nucleotide CTP de novo synthesis. Since 2010, a series of studies have demonstrated that CTPS can form filamentous structures in bacteria and eukaryotes, which are termed cytoophidia. However, it is unknown whether cytoophidia exist in the third domain of life, archaea. Using Haloarcula hispanica as a model system, here we demonstrate that CTPS forms distinct intracellular compartments in archaea. Under stimulated emission depletion microscopy, we find that the structures of H. hispanica CTPS are elongated, similar to cytoophidia in bacteria and eukaryotes. When Haloarcula cells are cultured in low-salt medium, the occurrence of cytoophidia increases dramatically. In addition, treatment of H. hispanica with a glutamine analog or overexpression of CTPS can promote cytoophidium assembly. Our study reveals that CTPS can form cytoophidia in all three domains of life, suggesting that forming cytoophidia is an ancient property of CTPS.

CTP合酶（CTPS）是一种重要的代谢酶，可催化核苷酸CTP从头合成的限速反应。自2010年以来，一系列研究表明CTPS可以在细菌和真核生物中形成丝状结构，称为胞吞。然而，尚不知道细胞吞噬作用是否存在于生命的第三域古细菌中。使用西班牙扁藻作为模型系统，在这里我们证明CTPS在古细菌中形成不同的细胞内区室。在受激发射耗竭显微镜下，我们发现西班牙血吸虫CTPS的结构被拉长，类似于细菌和真核生物中的细胞吞噬作用。当Halooccula细胞在低盐培养基中培养，细胞吞噬的发生率急剧增加。另外，用谷氨酰胺类似物治疗西班牙血吸虫或CTPS的过表达可促进细胞噬菌体组装。我们的研究表明，CTPS可以在生活的所有三个领域中形成细胞吞噬作用，这表明形成细胞吞噬作用是CTPS的古老特性。