Archaeal Biology Center, Institute for Advanced Study, Shenzhen University , Shenzhen, Guangdong, China.
Shenzhen Key Laboratory of Marine Microbiome Engineering, Institute for Advanced Study, Shenzhen University , Shenzhen, Guangdong, China.
mSystems. 2023 Aug 31;8(4):e0030523. doi: 10.1128/msystems.00305-23. Epub 2023 Jul 17.
Korarchaeota, due to its rarity in common environments, is one of the archaeal phyla that has received the least attention from researchers. It was previously thought to consist solely of strict thermophiles. However, our study provides genetic evidence for the presence of korarchaeal members in temperate subsurface seawater. Furthermore, a systematic reclassification of the Korarchaeota based on 16S rRNA genes and genomes has revealed three novel marine groups (Kor-6 to Kor-8) at the root of the Korarchaeota branch. Kor-6 contains microbes that are present in moderate temperatures. All three novel marine phyla possess genes for the Wood-Ljungdahl pathway, and Kor-7 and Kor-8 possess fewer genes encoding oxygen resistance traits than other korarchaeal groups, suggesting a distinct lifestyle for these novel phyla. Our results, together with estimations of Korarchaeota divergence times, suggest that oxygen availability may be one of the important factors that have influenced the evolution of Korarchaeota. IMPORTANCE Korarchaeota were previously thought to inhabit exclusively high-temperature environments. However, our study provides genetic evidence for their unexpected presence in temperate marine waters. Through analysis of publicly available korarchaeal reference data, we have systematically reclassified Korarchaeota and identified the existence of three previously unknown marine groups (Kor-6, Kor-7, and Kor-8) at the root of the Korarchaeota branch. Comparative analysis of their gene content revealed that these novel groups exhibit a lifestyle distinct from other Korarchaeota. Specifically, they have the ability to fix carbon exclusively via the Wood-Ljungdahl (WL) pathway, and the genomes within Kor-7 and Kor-8 contain few genes encoding antioxidant enzymes, indicating their strictly anaerobic lifestyle. Further studies suggest that the genes related to methane metabolism and the WL pathway may have been inherited from a common ancestor of the Korarchaeota and that oxygen availability may be one of the important evolutionary factors that shaped the diversification of this archaeal phylum.
古菌门，由于其在常见环境中的稀有性，是古菌门中受到研究人员关注最少的一门。以前，人们认为它仅由严格的嗜热菌组成。然而，我们的研究为古菌门成员存在于温带地下海水中提供了遗传证据。此外，基于 16S rRNA 基因和基因组对古菌门进行的系统重新分类，揭示了古菌门分支根部的三个新的海洋群（Kor-6 到 Kor-8）。Kor-6 含有存在于中等温度下的微生物。这三个新的海洋门都拥有 Wood-Ljungdahl 途径的基因，而 Kor-7 和 Kor-8 拥有的氧抗性基因比其他古菌门群体少，这表明这些新门具有独特的生活方式。我们的研究结果，以及对古菌门分歧时间的估计，表明氧气的可用性可能是影响古菌门进化的重要因素之一。
古菌门以前被认为只栖息在高温环境中。然而，我们的研究为它们在温带海洋水中的意外存在提供了遗传证据。通过分析公开的古菌参考数据，我们对古菌门进行了系统的重新分类，并在古菌门分支的根部发现了三个以前未知的海洋群（Kor-6、Kor-7 和 Kor-8）。对它们的基因内容进行比较分析表明，这些新的群体表现出与其他古菌门不同的生活方式。具体来说，它们具有通过 Wood-Ljungdahl（WL）途径专门固定碳的能力，并且 Kor-7 和 Kor-8 中的基因组含有很少编码抗氧化酶的基因，表明它们是严格的厌氧生活方式。进一步的研究表明，与甲烷代谢和 WL 途径相关的基因可能是从古菌门的共同祖先遗传下来的，氧气的可用性可能是塑造这个古菌门多样化的重要进化因素之一。
