Cyanobacteria - CNRS URA 2172  


  HEADDr. TANDEAU de MARSAC Nicole / nicole.tandeau-de-marsac@pasteur.fr
  MEMBERSBENEDIC Marie Bénédicte / COURSIN Thérèse / ESCOFFIER Nicolas / GAGET Virginie / Dr. GUGGER Muriel/ Dr. HUMBERT Jean François / LAURENT Thierry / SABART Marion / Dr. QUILLARDET Philippe / RIPPKA Rosmarie / TAMBOSCO Jennifer / VERGALLI Julia


  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. The PCC ("Pasteur Culture Collection of Cyanobacteria") 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 the 750 strains of the PCC and of the genomes of ten new Microcystis strains has been achieved (Coll. Génoscope, Evry).

Transcriptome analysis of Microcystis aeruginosa >PCC 7806 and of its toxin-less mutant. In order to elucidate the role of the hepatotoxic microcystins in cell metabolism and get deeper insights into the life cycle of M. aeruginosa, DNA chips were designed based on the genome sequence of strain PCC 7806 (Coll. Génopole-Pasteur). These DNA chips are currently used to globally compare gene expression of the wild-type toxic strain and the microcystin-deficient mutant, during a dark-light cycle and under various environmental conditions.

Population genetics of bloom-forming cyanobacteria. M. aeruginosa is able to bloom in a wide range of freshwater habitats. Molecular ecological studies showed that the genotype composition of M. aeruginosa populations in a French river and several reservoirs depends on very local, ecosystem-specific selection pressures. In contrast, no biogeographic differentiation between populations was found at the worldwide scale, most of the genotypes being ubiquitously distributed (Coll. Univ. Clermont-Ferrand).

Variations in the potential toxicity during cyanobacterial blooms. The concentration of microcystins (MCs) produced during blooms depends, for a large part, on variations in the proportion of strains containing the genes involved in the synthesis of these toxins. Based on field studies and laboratory experiments, we demonstrated that non-growth-limiting conditions led to the selection of non-MC-producing genotypes, whereas MC-producing genotypes were dominant under growth-limiting conditions. This suggests that the benefits of producing MCs outweigh their costs when cells are growth-limited (Coll. MNHN Paris).

Keywords: Cyanobacteria, biodiversity, waterbloom, hepatotoxin, microcystin

Pmic.jpg

Microcystis (Yvelines, France)



  Publications

  1. BRIAND E., GUGGER M., FRANÇOIS J.C., BERNARD C., HUMBERT J.F. & QUIBLIER C. 2008. Temporal variations in the dynamics of potentially microcystin-producing strains in a bloom-forming Planktothrix agardhii (cyanobacteria) population. Appl. Environ. Microbiol< 74, 3839-3848. PMID: 18441113.

  2. BRIANd e., Yépremian C., Humbert j.F. & QUIBLIER C. 2008. Comparative studies on the fitness of microcystin-producing and non-producing Planktothrix agardhii strains cultivated under different environmental conditions. Environ. Microbiol. 10, 3337-3348. PMID: 18759740.

  3. Cadel-Six S., Dauga C., Castets A.M., Rippka R., Bouchier C., Tandeau de Marsac N. & Welker M. 2008. Halogenase genes in nonribosomal peptide synthetase gene clusters of Microcystis (cyanobacteria): sporadic distribution and evolution. Mol. Biol. Evol. 25, 2031-41. PMID: 18614525.

  4. Dufresne A., Ostrowski M., Scanlan D.J., Garczarek L., Mazard S., Palenik B.P., Paulsen I.T., tandeau de Marsac N;, Wincker P., Dossat C., Ferriera S., Johnson J., Post A.F., Hess W.R., Partensky F. 2008. Unraveling the genomic mosaic of a ubiquitous genus of marine cyanobacteria. Genome Biol. 9, R90. PMID: 18507822.

  5. FrangeuL L., QuillardeT P., CastetS A.M., HumberT J.F., MatthijS H.C.P., CorteZ D., ToloneN A., ZhanG C.C., GribaldO S., KehR J.C., ZilligeS Y., ZiemerT N., BeckeR S., TallA E., LatifI A., BillaulT A., LepelletieR A., DittmanN E., BouchieR C. & Tandeau de MarsaC N. 2008. Highly plastic genome of Microcystis aeruginosa PCC 7806, a ubiquitous toxic freshwater cyanobacterium. BMC Genomics 9, 274. PMID: 18534010.





Activity Reports 2009 - Institut Pasteur
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