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UID:7985@i2m.univ-amu.fr
DTSTART;TZID=Europe/Paris:20151023T140000
DTEND;TZID=Europe/Paris:20151023T160000
DTSTAMP:20241210T142815Z
URL:https://www.i2m.univ-amu.fr/evenements/approaches-to-detect-and-classi
 fy-megavirales/
SUMMARY:Vikas Sharma (I2M\, Aix-Marseille Université): Approaches to detec
 t and classify Megavirales
DESCRIPTION:Vikas Sharma: -\nNucleocytoplasmic large DNA viruses (NCLDVs)\,
  or representatives from the proposed order Megavirales\, belong to famili
 es of giant viruses that infect a large number of eukaryotic hosts. This o
 rder includes families Mimiviridae\, Marseilleviridae\, Ascoviridae\, Irid
 oviridae\, Phycodnaviridae\, Poxviridae\, Asfarviridae\, and pandoraviruse
 s\, Pithovirus sibericum\, faustoviruses and Mollivirus sibericum that lik
 ely represents new viral families. These viruses have genomes whose size r
 anges from 100 kilobase to 2.5 megabase pairs and which have surprising ge
 ne contents and features\, which raised various questions about their orig
 in and evolution. Environmental metagenomic studies showed that there is a
  “dark matter”\, composed of sequences not linked to any known organis
 m. However\, sequence identification was mainly determined using ribosomal
  DNA (rDNA) sequences\, which led therefore to ignore viruses\, including 
 megaviruses\, because they are devoid of such genes. Core informational ge
 nes\, including DNA-dependant RNA polymerase (RNAP)\, are other markers th
 at appear as more appropriate for a comprehensive classification as they a
 re conserved in cellular organisms (Bacteria\, Archaea and Eukarya) and in
  Megavirales. For our phylogenetic analyses\, we have selected a represent
 ative set of cellular organisms using TimeTree. We used a small set of uni
 versally conserved genes that included RNAP and reconstructed ancestral se
 quences to search for megavirus relatives in sequence databases and to per
 form phylogeny reconstructions. This allowed identified three megaviral se
 quences that were misannotated as Hydra magnipapillata\, Marine group II E
 uryarcheota and Phytophthora parasitica\, and new viral clades in environm
 ental databases. In addition\, we delineated Megavirales as a fourth monop
 hylogenetic branch aside Bacteria\, Archaea and Eukarya\, which was named 
 TRUC (for Things Resisting Uncompleted Classification). Moreover\, we clas
 sified by phylogenetic and phyletic analyses based on informational genes 
 new giant viruses including pandoraviruses and Pithovirus sibericum as new
  bona fide members of the fourth TRUC. Our analyses shows that RNAP as wel
 l as a few other genes used in our studies allow a more comprehensive over
 view and classification of the biological diversity than rDNA\, that RNAP 
 can be an universal probe to uncover new viral sequences\, and that using 
 putative ancestral sequences recreated for conserved genes can identify di
 stant\, undescribed viral clades. Thus\, we detected hidden microbes and c
 lassified new Megavirales representatives.\n-\nKeywords : Giant virus\; Me
 gavirales\; NCLDV\; Informational genes\; TRUC\; Domains of life\; Phyloge
 ny\; Hierarchical clustering.\n-\n*Directeurs de thèse :\n-\n- Didier RAO
 ULT\, URMITE\, UMR7278\, Marseille\n- Pierre PONTAROTTI\, I2M\, Marseille\
 n-\n-\nLien : theses.fr
ATTACH;FMTTYPE=image/jpeg:https://www.i2m.univ-amu.fr/wp-content/uploads/2
 020/01/Vikas_Sharma.jpg
CATEGORIES:Soutenance de thèse,Mathématiques-Évolution-Biologie
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