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

<p>Abstract</p> <p>Background</p> <p>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.</p> <p>Results</p> <p>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.</p> <p>Conclusion</p> <p>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.</p

Evolutionary history of phosphatidylinositol- 3-kinases: ancestral origin in eukaryotes and complex duplication patterns

BACKGROUND: Phosphatidylinositol-3-kinases (PI3Ks) are a family of eukaryotic enzymes modifying phosphoinositides in phosphatidylinositols-3-phosphate. Located upstream of the AKT/mTOR signalling pathway, PI3Ks activate secondary messengers of extracellular signals. They are involved in many critical cellular processes such as cell survival, angiogenesis and autophagy. PI3K family is divided into three classes, including 14 human homologs. While class II enzymes are composed of a single catalytic subunit, class I and III also contain regulatory subunits. Here we present an in-depth phylogenetic analysis of all PI3K proteins. RESULTS: We confirmed that PI3K catalytic subunits form a monophyletic group, whereas regulatory subunits form three distinct groups. The phylogeny of the catalytic subunits indicates that they underwent two major duplications during their evolutionary history: the most ancient arose in the Last Eukaryotic Common Ancestor (LECA) and led to the emergence of class III and class I/II, while the second – that led to the separation between class I and II – occurred later, in the ancestor of Unikonta (i.e., the clade grouping Amoebozoa, Fungi, and Metazoa). These two major events were followed by many lineage specific duplications in particular in vertebrates, but also in various protist lineages. Major loss events were also detected in Vidiriplantae and Fungi. For the regulatory subunits, we identified homologs of class III in all eukaryotic groups indicating that, for this class, both the catalytic and the regulatory subunits were presents in LECA. In contrast, homologs of the regulatory class I have a more recent origin. CONCLUSIONS: The phylogenetic analysis of the PI3K shed a new light on the evolutionary history of these enzymes. We found that LECA already contained a PI3K class III composed of a catalytic and a regulatory subunit. Absence of class II regulatory subunits and the recent origin of class I regulatory subunits is puzzling given that the class I/II catalytic subunit was present in LECA and has been conserved in most present-day eukaryotic lineages. We also found surprising major loss and duplication events in various eukaryotic lineages. Given the functional specificity of PI3K proteins, this suggests dynamic adaptation during the diversification of eukaryotes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12862-015-0498-7) contains supplementary material, which is available to authorized users

A DNA topoisomerase IB in Thaumarchaeota testifies for the presence of this enzyme in the last common ancestor of Archaea and Eucarya

DNA topoisomerase IB (TopoIB) was thought for a long time to be a eukaryotic specific enzyme. A shorter version was then found in viruses and later on in several bacteria, but not in archaea. Here, we show that a eukaryotic-like TopoIB is present in the recently sequenced genomes of two archaea of the newly proposed phylum Thaumarchaeota. Phylogenetic analyses suggest that a TopoIB was present in the last common ancestor of Archaea and Eucarya. This finding indicates that the last common ancestor of Archaea and Eucarya may have harboured a DNA genome

Phylogenomic test of the hypotheses for the evolutionary origin of eukaryotes

International audienceThe evolutionary origin of eukaryotes is a question of great interest for which many different hypotheses have been proposed. These hypotheses predict distinct patterns of evolutionary relationships for individual genes of the ancestral eukaryotic genome. The availability of numerous completely sequenced genomes covering the three domains of life makes it possible to contrast these predictions with empirical data. We performed a systematic analysis of the phylogenetic relationships of ancestral eukaryotic genes with archaeal and bacterial genes. In contrast with previous studies, we emphasize the critical importance of methods accounting for statistical support, horizontal gene transfer, and gene loss, and we disentangle the processes underlying the phylogenomic pattern we observe. We first recover a clear signal indicating that a fraction of the bacteria-like eukaryotic genes are of alphaproteobacterial origin. Then, we show that the majority of bacteria-related eukaryotic genes actually do not point to a relationship with a specific bacterial taxonomic group. We also provide evidence that eukaryotes branch close to the last archaeal common ancestor. Our results demonstrate that there is no phylogenetic support for hypotheses involving a fusion with a bacterium other than the ancestor of mitochondria. Overall, they leave only two possible interpretations, respectively, based on the early-mitochondria hypotheses, which suppose an early endosymbiosis of an alphaproteobacterium in an archaeal host and on the slow-drip autogenous hypothesis, in which early eukaryotic ancestors were particularly prone to horizontal gene transfers

Phylogenomics of the archaeal flagellum: rare horizontal gene transfer in a unique motility structure

<p>Abstract</p> <p>Background</p> <p>As bacteria, motile archaeal species swim by means of rotating flagellum structures driven by a proton gradient force. Interestingly, experimental data have shown that the archaeal flagellum is non-homologous to the bacterial flagellum either in terms of overall structure, components and assembly. The growing number of complete archaeal genomes now permits to investigate the evolution of this unique motility system.</p> <p>Results</p> <p>We report here an exhaustive phylogenomic analysis of the components of the archaeal flagellum. In all complete archaeal genomes, the genes coding for flagellum components are co-localized in one or two well-conserved genomic clusters showing two different types of organizations. Despite their small size, these genes harbor a good phylogenetic signal that allows reconstruction of their evolutionary histories. These support a history of mainly vertical inheritance for the components of this unique motility system, and an interesting possible ancient horizontal gene transfer event (HGT) of a whole flagellum-coding gene cluster between Euryarchaeota and Crenarchaeota.</p> <p>Conclusion</p> <p>Our study is one of the few exhaustive phylogenomics analyses of a non-informational cell machinery from the third domain of life. We propose an evolutionary scenario for the evolution of the components of the archaeal flagellum. Moreover, we show that the components of the archaeal flagellar system have not been frequently transferred among archaeal species, indicating that gene fixation following HGT can also be rare for genes encoding components of large macromolecular complexes with a structural role.</p

Happy together: genomic insights into the unique Nanoarchaeum/Ignicoccus association

The complete genome sequence of the crenarchaeon Ignicoccus hospitalis published recently in Genome Biology provides a great leap forward in the dissection of its unique association with another hyperthermophilic archaeon, Nanoarchaeum equitans

Article 5. L’émergence des eucaryotes : une mosaïque d’ADN

International audienceTout organisme sur Terre appartient à l'une des trois branches du vivant : bactéries, archées ou eucaryotes. Au-delà de caractères qui lui sont propres, la lignée des eucaryotes, dont l'homme est issu, partage à la fois des caractères d'archées et de bactéries. La génomique révèle les multiples origines de l'ADN des eucaryotes

Iron-Sulfur (Fe/S) Protein Biogenesis: Phylogenomic and Genetic Studies of A-Type Carriers

Iron sulfur (Fe/S) proteins are ubiquitous and participate in multiple biological processes, from photosynthesis to DNA repair. Iron and sulfur are highly reactive chemical species, and the mechanisms allowing the multiprotein systems ISC and SUF to assist Fe/S cluster formation in vivo have attracted considerable attention. Here, A-Type components of these systems (ATCs for A-Type Carriers) are studied by phylogenomic and genetic analyses. ATCs that have emerged in the last common ancestor of bacteria were conserved in most bacteria and were acquired by eukaryotes and few archaea via horizontal gene transfers. Many bacteria contain multiple ATCs, as a result of gene duplication and/or horizontal gene transfer events. Based on evolutionary considerations, we could define three subfamilies: ATC-I, -II and -III. Escherichia coli, which has one ATC-I (ErpA) and two ATC-IIs (IscA and SufA), was used as a model to investigate functional redundancy between ATCs in vivo. Genetic analyses revealed that, under aerobiosis, E. coli IscA and SufA are functionally redundant carriers, as both are potentially able to receive an Fe/S cluster from IscU or the SufBCD complex and transfer it to ErpA. In contrast, under anaerobiosis, redundancy occurs between ErpA and IscA, which are both potentially able to receive Fe/S clusters from IscU and transfer them to an apotarget. Our combined phylogenomic and genetic study indicates that ATCs play a crucial role in conveying ready-made Fe/S clusters from components of the biogenesis systems to apotargets. We propose a model wherein the conserved biochemical function of ATCs provides multiple paths for supplying Fe/S clusters to apotargets. This model predicts the occurrence of a dynamic network, the structure and composition of which vary with the growth conditions. As an illustration, we depict three ways for a given protein to be matured, which appears to be dependent on the demand for Fe/S biogenesis

Characterization of Halorubrum sfaxense sp. nov., a New Halophilic Archaeon Isolated from the Solar Saltern of Sfax in Tunisia

An extremely halophilic archaeon, strain ETD6, was isolated from a marine solar saltern in Sfax, Tunisia. Analysis of the 16S rRNA gene sequence showed that the isolate was phylogenetically related to species of the genus Halorubrum among the family Halobacteriaceae, with a close relationship to Hrr. xinjiangense (99.77% of identity). However, value for DNA-DNA hybridization between strain ETD6 and Hrr.xinjiangense were about 24.5%. The G+C content of the genomic DNA was 65.1 mol% (T(m)). Strain ETD6 grew in 15–35% (w/v) NaCl. The temperature and pH ranges for growth were 20–55°C and 6–9, respectively. Optimal growth occurred at 25% NaCl, 37°C, and pH 7.4. The results of the DNA hybridization against Hrr. xinjiangense and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain ETD6 from other Hrr. species. Therefore, strain ETD6 represents a novel species of the genus Halorubrum, for which the name Hrr. sfaxense sp. nov. is proposed. The Genbank EMBL-EBI accession number is GU724599

The TERB1-TERB2-MAJIN complex of mouse meiotic telomeres dates back to the common ancestor of metazoans

International audienceBackground: Meiosis is essential for sexual reproduction and generates genetically diverse haploid gametes from a diploid germ cell. Reduction of ploidy depends on active chromosome movements during early meiotic prophase I. Chromosome movements require telomere attachment to the nuclear envelope. This attachment is mediated by telomere adaptor proteins. Telomere adaptor proteins have to date been identified in fission yeast and mice. In the mouse, they form a complex composed of the meiotic proteins TERB1, TERB2, and MAJIN. No sequence similarity was observed between these three mouse proteins and the adaptor proteins of fission yeast, raising the question of the evolutionary history and significance of this specific protein complex. Result: Here, we show the TERB1, TERB2, and MAJIN proteins are found throughout the Metazoa and even in earlybranching non-bilateral phyla such as Cnidaria, Placozoa and Porifera. Metazoan TERB1, TERB2, and MAJIN showed comparable domain architecture across all clades. Furthermore, the protein domains involved in the formation of the complex as well as those involved for the interaction with the telomere shelterin protein and the LINC complexes revealed high sequence similarity. Finally, gene expression in the cnidarian Hydra vulgaris provided evidence that the TERB1-TERB2-MAJIN complex is selectively expressed in the germ line. Conclusion: Our results indicate that the TERB1-TERB2-MAJIN complex has an ancient origin in metazoans, suggesting conservation of meiotic functions