unveiling fungal zooflagellates as members of freshwater picoeukaryotes: evidence from a molecular...
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Unveiling fungal zooflagellates as members of
freshwater picoeukaryotes: evidence from a molecular
diversity study in a deep meromictic lake
Lefèvre et al., 2007
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Etude de la biodiversité de picoeucaryotes
basée sur des méthodes moléculaires au Lac Pavin
Exposé présenté par:HAMOUDA Amine
Lojou Vincent
Etudiants en Master I – COM
U33: Diversité des Organismes Marins
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Lac PavinGéographiquement:
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Il est né d'une explosion volcanique qui creusa le flanc du puy
de Montchal.
De forme presque circulaire, surface de 44ha, profondeur max
est de 92m, enchâssé dans une forêt, et influence anthropique
relativement faible.
Lac Pavin
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Procédé expérimental
Filtration: On n’a gardé que les organismes de taille <5µm
L’échantillonnage à des profondeurs variables:
5m (épilimnion)
9-10m (métalimnion)
56-59 m (oxycline)
30 m (hypolimnion)
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Procédé expérimental
Extraction d’ADN + Amplification par PCR
Construction de l’arbre phylogénique
Détection des ADNr 18S
Détermination des affiliations phylogéniques, calcul des distances et alignement par des méthodes Bioinformatiques.
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Profil vertical de température, d'oxygène et de Chlorphylle a mesurés le 310804 au Lac Pavin
Profil vertical de température, d'oxygène et de Chlorophylle a mesurés le 061004 au Lac Pavin
T(°C), O2 (mg l–1) T(°C), O2 (mg l–1)
Chl a (μg l–1) Chl a (μg l–1)
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Arbre Phylogénétique
Nouveau clade 1: Asteronella formosa un Diatomée parasité par un Rhizophydium
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Nouveau clade 4 est frère des Euglypha rotunda
Euglypha spEuglypha rotunda
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Nouveau clade 5 fait parti des Perkinsea, ici une espèce qui parasite un bivalve: philippinarum
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Courbes de raréfaction
Sont obtenus par extrapolation des valeurs d’OTU en fonction du nombre de clones, via des outils informatiques.
Le palier est synonymes de biodiversité maximale atteinte.
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Zone oxique 061004
Zone oxique du 310804
Zone oxycline 061004
Zone oxycline 310804
Courbes de raréfaction
Nombre de clones
% O
TU
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Courbes de raréfaction
Biodiversité maximale atteinte:
310804: en oxycline (50-60 m)
061004: en zone oxique( 0-60 m)
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Abondance relative310804
Abo
ndan
ce e
n %
Zone oxique
Oxycline
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061004Abondance relative
Abo
ndan
ce e
n %
Zone oxique
Oxycline
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Conclusion
La communauté du lac Pavin est unique:
Meromictie
Biodiversité découverte avec 5 nouveaux clades
Le parasitisme est important dans la communauté des picoeucaryotes, et influence sur les producteurs primaires.
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Conclusion
Diversité très variable en fonction de la saison.
2 écosystèmes dans le lac Pavin: Oxycline
La zone oxique
Les populations sont différentes en comparaison avec d’autres études sur des lacs.
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Une grande diversité des picoeucaryotes est à découvrir.
Conclusion
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Critiques
Les valeurs de Bootstrap sont parfois illisibles, ceci ne nous permet pas de discuter la solidité de l’arbre.
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Critiques
Certains graphiques sont difficilement lisibles.
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La méthode est basée uniquement sur les phylogénies moléculaires
Utilisation d’autres marqueurs moléculaires pour renforcer la phylogénie.
L’écosystème des nouveaux clades découverts?
Critiques
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FIN
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Bibliographie
http://www.env.sci.toho-u.ac.jp/topics/009204.html
http://commons.wikimedia.org/wiki/Image:Euglypha_sp.jpg
http://www.pac.dfo-mpo.gc.ca/sci/shelldis/pages/perkincc_e.htm
Olive P., BoulègueJ. ;étude biogéochimique d'un lac méromictique :le lac Pavin, France;Géomorphologie : relief, processus, environnement, 2004, n° 4, p. 305-316.
http://protist.i.hosei.ac.jp/PDB6/PCD0222/htmls/35.html
http://www.com.univ-mrs.fr/~boudouresque