School of Biological Sciences, University of Bristol, United Kingdom.
School of Earth Sciences, University of Bristol, United Kingdom.
Genome Biol Evol. 2019 Mar 1;11(3):883-898. doi: 10.1093/gbe/evz034.
One of the key differences between Bacteria and Archaea is their canonical membrane phospholipids, which are synthesized by distinct biosynthetic pathways with nonhomologous enzymes. This "lipid divide" has important implications for the early evolution of cells and the type of membrane phospholipids present in the last universal common ancestor. One of the main challenges in studies of membrane evolution is that the key biosynthetic genes are ancient and their evolutionary histories are poorly resolved. This poses major challenges for traditional rooting methods because the only available outgroups are distantly related. Here, we address this issue by using the best available substitution models for single-gene trees, by expanding our analyses to the diversity of uncultivated prokaryotes recently revealed by environmental genomics, and by using two complementary approaches to rooting that do not depend on outgroups. Consistent with some previous analyses, our rooted gene trees support extensive interdomain horizontal transfer of membrane phospholipid biosynthetic genes, primarily from Archaea to Bacteria. They also suggest that the capacity to make archaeal-type membrane phospholipids was already present in last universal common ancestor.
细菌和古菌的一个关键区别在于它们的典型膜脂，这些膜脂由不同的生物合成途径合成，具有非同源酶。这种“脂质分裂”对细胞的早期进化以及最后一个普遍共同祖先中存在的膜脂类型有重要影响。膜进化研究的主要挑战之一是关键生物合成基因非常古老，它们的进化历史难以确定。这对传统的系统发育分析方法提出了重大挑战，因为唯一可用的外群与它们的亲缘关系非常远。在这里，我们通过使用单基因树的最佳替代模型、扩展分析到最近环境基因组学揭示的未培养原核生物多样性，以及使用两种不依赖外群的互补方法来解决这个问题。与一些先前的分析一致，我们的有根基因树支持膜脂生物合成基因的广泛跨域水平转移，主要是从古菌到细菌。它们还表明，制造古菌型膜脂的能力在最后一个普遍共同祖先中就已经存在。
