Giant viruses, giant chimeras: the multiple evolutionary histories of Mimivirus genes - PubMed (original) (raw)

Giant viruses, giant chimeras: the multiple evolutionary histories of Mimivirus genes

David Moreira et al. BMC Evol Biol. 2008.

Abstract

Background: Although capable to evolve, viruses are generally considered non-living entities because they are acellular and devoid of metabolism. However, the recent publication of the genome sequence of the Mimivirus, a giant virus that parasitises amoebas, strengthened the idea that viruses should be included in the tree of life. In fact, the first phylogenetic analyses of a few Mimivirus genes that are also present in cellular lineages suggested that it could define an independent branch in the tree of life in addition to the three domains, Bacteria, Archaea and Eucarya.

Results: We tested this hypothesis by carrying out detailed phylogenetic analyses for all the conserved Mimivirus genes that have homologues in cellular organisms. We found no evidence supporting Mimivirus as a new branch in the tree of life. On the contrary, our phylogenetic trees strongly suggest that Mimivirus acquired most of these genes by horizontal gene transfer (HGT) either from its amoebal hosts or from bacteria that parasitise the same hosts. The detection of HGT events involving different eukaryotic donors suggests that the spectrum of hosts of Mimivirus may be larger than currently known.

Conclusion: The large number of genes acquired by Mimivirus from eukaryotic and bacterial sources suggests that HGT has been an important process in the evolution of its genome and the adaptation to parasitism.

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Figures

Figure 1

Figure 1

Taxonomic distribution of 128 conserved mimiviral ORFs. The number of homologues in the three domains of life (Eucarya, Archaea and Bacteria) is shown.

Figure 2

Figure 2

Bayesian phylogenetic trees of (A) the Zn-dependent alcohol dehydrogenase (MIMI_L498) and of (B) the putative outer membrane lipoprotein (MIMI_R877). These trees show HGT events from Proteobacteria that co-exist with Mimivirus within the same amoebal hosts. Numbers at nodes are Bayesian posterior probabilities. Scale bar represents the number of estimated changes per position for a unit of branch length.

Figure 3

Figure 3

Bayesian phylogenetic tree of three serine/threonine protein kinases (MIMI_R818, MIMI_R826, MIMI_R831). The tree shows one gene acquisition by Mimivirus from its host, followed by two duplication events in the mimiviral lineage. Numbers at nodes are Bayesian posterior probabilities. Scale bar represents the number of estimated changes per position for a unit of branch length.

Figure 4

Figure 4

Bayesian phylogenetic tree of a cytosolic- and an endoplasmic reticulum (ER)-type HSP70 heat shock protein (MIMI_L254, and MIMI_L393). The tree shows the eukaryotic origin of the two mimiviral HSP70 by independent HGT from two distant eukaryotic groups (Amoebozoa and Heterolobosea). Numbers at nodes are Bayesian posterior probabilities. Scale bar represents the number of estimated changes per position for a unit of branch length.

Figure 5

Figure 5

Bayesian phylogenetic tree of the GDP mannose 4,6-dehydratase (MIMI_R141). The tree shows a case of gene acquisition by Mimivirus from a euglenozoan donor. Numbers at nodes are Bayesian posterior probabilities. Scale bar represents the number of estimated changes per position for a unit of branch length.

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