Cyanobacteria - CNRS URA 2172  


  HEADDr. TANDEAU de MARSAC Nicole / ntmarsac@pasteur.fr
  MEMBERSBOUSSIER Amandine / CADEL-SIX Sabrina / COURSIN Thérèse / GAGET Virginie / Dr. GUGGER Muriel/ Dr. HUMBERT Jean François / LAURENT Thierry / LENOIR Lucile
Dr. MEJEAN Annick / SABART Marion / Dr. PEYRAUD-THOMAS Caroline /Dr. QUILLARDET Philippe / RIPPKA Rosmarie


  Annual Report

Cyanobacteria, oxygenic photosynthetic prokaryotes, largely contribute to the balance between CO2 and O2 in the atmosphere. Adapted to a wide range of environmental conditions, they colonize most ecosystems. Bloom formation in continental freshwater environments disrupt the equilibrium of these ecosystems and may be harmful to animals and Man. Our research program aims at increasing our knowledge of the diversity, ecology and physiology of cyanobacteria and to develop molecular tools for assessment of the risks associated with the presence of toxic strains in water resources.

Biodiversity of cyanobacteria. These studies from gene to ecosystem rely on the analysis of environmental samples and on the PCC ("Pasteur Culture Collection of Cyanobacteria") that houses more than 750 axenic strains isolated from very diverse habitats. The mission of the PCC (certified ISO9001 v2000) includes both research and service activities (acquisition and preservation; sales of strains and consultation). The sequencing of the 16S rDNA of all the PCC strains is in progress, as well as the complete genome sequencing of several Microcystis strains (Coll. Génoscope, Evry).

Based on 950 ITS sequences, we studied the temporal and spatial diversity of Microcystis populations in six French freshwater ecosystems. The influence of local environmental conditions on the selection of the dominant genotypes in these populations was evidenced. At a worldwide scale, no phylogeographical clustering was found.

Genome sequence of Microcystis aeruginosa PCC 7806. This genome is characterized by a high plasticity with an unexpected high percentage of long repeated regions, putative transposases and restriction enzymes. No synteny was observed with other cyanobacterial genomes. Among other interesting features, the recent acquisition of eukaryotic-type actin and profilin genes located on a genomic island could be deduced. The location of this actin at the cell surface might play a role in cell stability. Six clusters of genes encoding five non-ribosomal peptide synthetases and/or polyketide synthases, and one ribosomally produced precursor, are involved in the synthesis of secondary metabolites, including two novel ones. Two of these metabolites are halogenated and phylogenetic analyses of the halogenase genes strongly suggest that they have been acquired by lateral gene transfer from a bacterium other than a cyanobacterium.

Pmic.jpg

Microcystis colonies and a single Microcystis cell (centre) showing actin at the cell surface (green circle); "genomic island" with the actin and profilin genes (actM and pfnM).



  Publications

Gugger M., Molica R., Le Berre B., Dufour P., Bernard C. and J.-F. Humbert (2005b). Genetic diversity of Cylindrospermopsis strains (cyanobacteria) isolated from four continents. Appl. Environ. Microbiol. 71 :1097-1100

Kehr J.C., Zilliges Y., Springer A., Disney M.D., Ratner D.D., Bouchier C., Seeberger P.H., Tandeau de Marsac N. and E. Dittmann (2006). A mannan binding lectin is involved in cell-cell attachment in a toxic strain of Microcystis aeruginosa. Mol. Microbiol. 59:893-906

Carré-Mlouka A., Méjean A., Quillardet P., Ashida H., Saito, Y., Yokota A., Callebaut, I., Sekowska A., Dittmann E. and C. Bouchier (2006). A new Rubisco-like protein coexists with a photosynthetic Rubisco in the planktonic cyanobacteria Microcystis. J. Biol. Chem. 281:24462-24471

Guljamow A., Jenke-Kodama H., Saumweber H., Quillardet P., Frangeul L., Castets A.M., Bouchier C., Tandeau de Marsac N.and E. Dittmann (2007) Horizontal gene transfer of two cytosceletal elements from a eukaryote to a cyanobacterium. Curr. Biol. 17: R757–R759

Cadel-Six, S., Peyraud-Thomas, C., Rippka, R., Brient, L., Tandeau de Marsac, N.,and Méjean A. Different genotypes of Anatoxin Producing Cyanobacteria co-exist in the Tarn river, France. Applied Environ. Microbiol. 73: 7605-7614





Activity Reports 2007 - Institut Pasteur
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