Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
Biol Direct. 2013 Apr 22;8:9. doi: 10.1186/1745-6150-8-9.
A single cultured marine organism, Nanoarchaeum equitans, represents the Nanoarchaeota branch of symbiotic Archaea, with a highly reduced genome and unusual features such as multiple split genes.
The first terrestrial hyperthermophilic member of the Nanoarchaeota was collected from Obsidian Pool, a thermal feature in Yellowstone National Park, separated by single cell isolation, and sequenced together with its putative host, a Sulfolobales archaeon. Both the new Nanoarchaeota (Nst1) and N. equitans lack most biosynthetic capabilities, and phylogenetic analysis of ribosomal RNA and protein sequences indicates that the two form a deep-branching archaeal lineage. However, the Nst1 genome is more than 20% larger, and encodes a complete gluconeogenesis pathway as well as the full complement of archaeal flagellum proteins. With a larger genome, a smaller repertoire of split protein encoding genes and no split non-contiguous tRNAs, Nst1 appears to have experienced less severe genome reduction than N. equitans. These findings imply that, rather than representing ancestral characters, the extremely compact genomes and multiple split genes of Nanoarchaeota are derived characters associated with their symbiotic or parasitic lifestyle. The inferred host of Nst1 is potentially autotrophic, with a streamlined genome and simplified central and energetic metabolism as compared to other Sulfolobales.
Comparison of the N. equitans and Nst1 genomes suggests that the marine and terrestrial lineages of Nanoarchaeota share a common ancestor that was already a symbiont of another archaeon. The two distinct Nanoarchaeota-host genomic data sets offer novel insights into the evolution of archaeal symbiosis and parasitism, enabling further studies of the cellular and molecular mechanisms of these relationships.
This article was reviewed by Patrick Forterre, Bettina Siebers (nominated by Michael Galperin) and Purification Lopez-Garcia.
单一培养的海洋生物纳古菌代表共生古菌的纳米古菌分支，具有高度简化的基因组和多个分裂基因等不寻常特征。
从黄石国家公园热特征 Obsidian Pool 中分离到的第一个陆地嗜热纳米古菌成员，通过单细胞分离进行分离，并与假定的宿主 Sulfolobales 古菌一起测序。新的纳米古菌（Nst1）和 N. equitans 都缺乏大多数生物合成能力，核糖体 RNA 和蛋白质序列的系统发育分析表明，两者形成了一个深分支古菌谱系。然而，Nst1 基因组超过 20%，并且编码完整的糖异生途径以及完整的古菌鞭毛蛋白。由于基因组较大，编码分裂蛋白的基因种类较少，并且没有分裂的非连续 tRNA，Nst1 似乎经历了比 N. equitans 更少的基因组减少。这些发现表明，纳米古菌极其紧凑的基因组和多个分裂基因不是原始特征，而是与其共生或寄生生活方式相关的衍生特征。与其他 Sulfolobales 相比，Nst1 的推断宿主可能是自养的，其基因组简化，中心和能量代谢简化。
N. equitans 和 Nst1 基因组的比较表明，海洋和陆地纳米古菌谱系共享一个已经是另一个古菌共生体的共同祖先。这两个不同的纳米古菌-宿主基因组数据集为古菌共生和寄生的进化提供了新的见解，使我们能够进一步研究这些关系的细胞和分子机制。
本文由 Patrick Forterre、Bettina Siebers（由 Michael Galperin 提名）和 Purification Lopez-Garcia 进行了评审。
