title: Alpha proteobacterial ancestry of the [Fe-Fe]-hydrogenases in anaerobic eukaryotes.
abstract: Eukaryogenesis, a major transition in evolution of life, originated from the symbiogenic fusion of an archaea with a metabolically versatile bacterium. By general consensus, the latter organism belonged to α proteobacteria, subsequently evolving into the mitochondrial organelle of our cells. The consensus is based upon genetic and metabolic similarities between mitochondria and aerobic α proteobacteria but fails to explain the origin of several enzymes found in the mitochondria-derived organelles of anaerobic eukaryotes such as Trichomonas and Entamoeba. These enzymes are thought to derive from bacterial lineages other than α proteobacteria, e.g., Clostridium - an obligate anaerobe. [FeFe]-hydrogenase constitues the characteristic enzyme of this anaerobic metabolism and is present in different types also in Entamoeba and other anaerobic eukaryotes. Here we show that α proteobacteria derived from metagenomic studies possess both the cytosolic and organellar type of [FeFe]-hydrogenase, as well as all the proteins required for hydrogenase maturation. These organisms are related to cultivated members of the Rhodospirillales order previously suggested to be close relatives of mitochondrial ancestors. For the first time, our evidence supports an α proteobacterial ancestry for both the anaerobic and the aerobic metabolism of eukaryotes.
  
  
  
  This article was reviewed by William Martin and Nick Lane, both suggested by the Authors.
authors.affiliation: Italian Institute of Technology, Via Morego 30, 16136, Genoa, Italy. mauro.degliesposti@iit.it.|Center for Genomic Sciences, UNAM Cuernavaca, Cuernavaca, Mexico. mauro.degliesposti@iit.it.
authors.forename: Mauro
authors.initials: M
authors.lastname: Degli Esposti
authors.affiliation: Center for Genomic Sciences, UNAM Cuernavaca, Cuernavaca, Mexico.
authors.forename: Diego
authors.initials: D
authors.lastname: Cortez
authors.affiliation: Center for Genomic Sciences, UNAM Cuernavaca, Cuernavaca, Mexico.
authors.forename: Luis
authors.initials: L
authors.lastname: Lozano
authors.affiliation: Department of Systems Biology, Center for Biological Sequence Analysis, Technical University of Denmark, Kemitorvet, Building 208, 2800, Kongens Lyngby, Denmark.
authors.forename: Simon
authors.initials: S
authors.lastname: Rasmussen
authors.affiliation: Department of Systems Biology, Center for Biological Sequence Analysis, Technical University of Denmark, Kemitorvet, Building 208, 2800, Kongens Lyngby, Denmark.
authors.forename: Henrik Bjørn
authors.initials: HB
authors.lastname: Nielsen
authors.affiliation: Center for Genomic Sciences, UNAM Cuernavaca, Cuernavaca, Mexico.
authors.forename: Esperanza
authors.initials: E
authors.lastname: Martinez Romero
mesh_terms: D020561:Alphaproteobacteria / Q000235:genetics*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D019143:Evolution, Molecular; D000069196:Gastrointestinal Microbiome / Q000235:genetics*; D006801:Humans; D006864:Hydrogenase / Q000235:genetics*; D010802:Phylogeny; D012244:Rhodospirillaceae / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D006864:Hydrogenase
keywords: Anaerobic metabolism; Bioenergetics; Eukaryogenesis; Mitochondria; [FeFe]-hydrogenase