title: A phylogenetic approach to the early evolution of autotrophy: the case of the reverse TCA and the reductive acetyl-CoA pathways.
abstract: In recent decades, a number of hypotheses on the autotrophic origin of life have been presented. These proposals invoke the emergence of reaction networks leading from CO or CO₂ to the organic molecules required for life. It has also been suggested that the last (universal) common ancestor (LCA or LUCA) of all extant cell lineages was a chemolitho-autotrophic thermophilic anaerobe. The antiquity of some carbon fixation pathways, the phylogenetic basal distribution of some autotrophic organisms, and the catalytic properties of iron-sulfur minerals have been advanced in support of these ideas. Here we critically examine the phylogenetic distribution and evolution of enzymes that are essential for two of the most ancient autotrophic means of metabolism: the reductive tricarboxylic acid (rTCA) cycle and the reductive acetyl-CoA pathway. Phylogenetic analysis of citryl-CoA synthetase and of citryl-CoA lyase, key enzymatic components of the rTCA cycle, and of CO dehydrogenase/acetyl-CoA synthase, a key enzyme in the reductive acetyl-CoA pathway, revealed that all three enzymes have undergone major lateral transfer events and therefore cannot be used as proof of the LCA's metabolic abilities nor as evidence of an autotrophic origin of life.
authors.affiliation: School of Sciences, National Autonomous University of Mexico, Mexico DF, Mexico.
authors.forename: Arturo
authors.initials: A
authors.lastname: Becerra
authors.affiliation: School of Sciences, National Autonomous University of Mexico, Mexico DF, Mexico.
authors.forename: Mario
authors.initials: M
authors.lastname: Rivas
authors.affiliation: Department of Biochemistry and Molecular Biology and Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: García-Ferris
authors.affiliation: School of Sciences, National Autonomous University of Mexico, Mexico DF, Mexico.
authors.forename: Antonio
authors.initials: A
authors.lastname: Lazcano
authors.affiliation: Department of Biochemistry and Molecular Biology and Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain.
authors.forename: Juli
authors.initials: J
authors.lastname: Peretó
mesh_terms: D000105:Acetyl Coenzyme A / Q000235:genetics* / Q000378:metabolism; D052818:Autotrophic Processes; D001419:Bacteria / Q000145:classification* / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D005075:Biological Evolution; D002952:Citric Acid Cycle; D008969:Molecular Sequence Data; D010802:Phylogeny; D014233:Tricarboxylic Acids / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D014233:Tricarboxylic Acids; D000105:Acetyl Coenzyme A
keywords: Wood–Ljungdahl pathway; autotrophic pathways; last common ancestor (LCA, LUCA); origin of life; reverse Krebs cycle