![]() ![]() Canonically, Archaea have isoprenoid chains attached to a glycerol-1-phosphate (G1P) backbone via ether bonds and can have either membrane spanning or bilayer-forming phospholipids ( Lombard et al. One striking difference is in the phospholipid composition of the cell membranes ( fig. 1), which is particularly important for understanding the origin of cellular life. 1997), and cell wall compositions ( Kandler 1995). These differences include DNA replication ( Kelman and Kelman 2014), transcription ( Bell and Jackson 1998), DNA packaging ( Reeve et al. 2016) strongly suggest that Archaea and Bacteria descend from a universal common ancestor (LUCA), they also differ in ways that have important implications for the early evolution of cellular life. Although similarities in their fundamental genetics and biochemistry, and evidence of homology in a near-universally conserved core of genes ( Weiss et al. Lipid divide, lipid evolution, phylogenetics, outgroup-free rooting IntroductionĪrchaea and Bacteria form the two primary domains of life (reviewed in Williams et al. They also suggest that the capacity to make archaeal-type membrane phospholipids was already present in last universal common ancestor. Consistent with some previous analyses, our rooted gene trees support extensive interdomain horizontal transfer of membrane phospholipid biosynthetic genes, primarily from Archaea to Bacteria. 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. This poses major challenges for traditional rooting methods because the only available outgroups are distantly related. 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 “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 key differences between Bacteria and Archaea is their canonical membrane phospholipids, which are synthesized by distinct biosynthetic pathways with nonhomologous enzymes. ![]()
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