Horizontal gene flow from Eubacteria to Archaebacteria and what it means for our understanding of eukaryogenesis.
The origin of the eukaryotic cell is considered one of the major evolutionary transitions in the history of life. Current evidence strongly supports a scenario of eukaryotic origin in which two prokaryotes, an archaebacterial host and an α-proteobacterium (the free-living ancestor of the mitochondrion), entered a stable symbiotic relationship. The establishment of this relationship was associated with a process of chimerization, whereby a large number of genes from the α-proteobacterial symbiont were transferred to the host nucleus. A general framework allowing the conceptualization of eukaryogenesis from a genomic perspective has long been lacking. Recent studies suggest that the origins of several archaebacterial phyla were coincident with massive imports of eubacterial genes. Although this does not indicate that these phyla originated through the same process that led to the origin of Eukaryota, it suggests that Archaebacteria might have had a general propensity to integrate into their genomes large amounts of eubacterial DNA. We suggest that this propensity provides a framework in which eukaryogenesis can be understood and studied in the light of archaebacterial ecology. We applied a recently developed supertree method to a genomic dataset composed of 392 eubacterial and 51 archaebacterial genera to test whether large numbers of genes flowing from Eubacteria are indeed coincident with the origin of major archaebacterial clades. In addition, we identified two potential large-scale transfers of uncertain directionality at the base of the archaebacterial tree. Our results are consistent with previous findings and seem to indicate that eubacterial gene imports (particularly from δ-Proteobacteria, Clostridia and Actinobacteria) were an important factor in archaebacterial history. Archaebacteria seem to have long relied on Eubacteria as a source of genetic diversity, and while the precise mechanism that allowed these imports is unknown, we suggest that our results support the view that processes comparable to those through which eukaryotes emerged might have been common in archaebacterial history.
School of Biological Sciences and School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol BS8 1TG, UK Department of Biology, National University of Ireland, Maynooth, Co. Kildare, Ireland Department of Life Science, The Natural History Museum, London SW7 5BD, UK.
Wasiu A
WA
Akanni
School of Biological Sciences and School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol BS8 1TG, UK Department of Biology, National University of Ireland, Maynooth, Co. Kildare, Ireland Department of Life Science, The Natural History Museum, London SW7 5BD, UK Institute of Biological, Environmental and Rural Sciences (IBERS), Aberystwyth University, Aberystwyth, Ceredigion SY23 3FG, UK.
Karen
K
Siu-Ting
Institute of Biological, Environmental and Rural Sciences (IBERS), Aberystwyth University, Aberystwyth, Ceredigion SY23 3FG, UK.
Christopher J
CJ
Creevey
Department of Biology, National University of Ireland, Maynooth, Co. Kildare, Ireland Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
James O
JO
McInerney
Department of Life Science, The Natural History Museum, London SW7 5BD, UK.
Mark
M
Wilkinson
Department of Life Science, The Natural History Museum, London SW7 5BD, UK.
Peter G
PG
Foster
School of Biological Sciences and School of Earth Sciences, University of Bristol, Life Sciences Building, Bristol BS8 1TG, UK davide.pisani@bristol.ac.uk.
Davide
D
Pisani
D001419:Bacteria / Q000235:genetics*; D005075:Biological Evolution; D051456:Gene Flow; D016680:Genome, Bacterial; D008957:Models, Genetic
Archaebacteria; Bayesian supertrees; symbiosis; tree of life