Cyanobacteria - CNRS URA2172  

  HEADProf. TANDEAU de MARSAC Nicole /
  MEMBERSCADEL-SIX Sabrina / GAGET Virginie / Dr HUMBERT Jean François / Dr MEJEAN Annick

  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. The occurrence of waterblooms in continental aquatic ecosystems disrupt their equilibrium 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 risk assessment 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 includes both research and service activities (preservation and development of biological resources; sales of strains and consultation). Being under quality control, the PCC was certified ISO9001 v2000 in 2006. New axenic neurotoxic Oscillatoria and hepatotoxic Microcystis strains were recently included in the PCC. In the context of an R & D Project (Veolia-Eau/GeneSystems/IP), a system for the rapid and reliable detection and identification of three genera of hepatotoxic cyanobacteria has been developed (Declaration of Intend, 2006). Its application will be highly useful to monitor health risk in drinking-water reservoirs. Four genome sequencing projects are in progress for strains of the PCC including the hepatotoxic strain Microcystis PCC 7806 (Coll. Genopole-IP; Génoscope; Moore Foundation).

Molecular mechanisms controlling waterblooms. In silico analysis of the Microcystis genome revealed the existence of genes sharing similarities with those encoding proteins involved in apoptosis in eukaryotes. This process might be involved in the disappearance of Microcystis blooms in nature. We are initiating transcriptomic studies to evaluate the physiological changes during the life cycle of Microcystis and the acclimation capacities of this cyanobacterium to grow in different environments.

Hepato- and neurotoxins. The proportion of microcystin producing and non-producing clones has been shown to vary during Microcystis and Planktothrix blooms in French lakes. A negative correlation has been established between cell abundance and the proportion of toxic clones. As assessed by an experimental approach, production of toxins seems more costly for the toxic clones under optimal than under sub-optimal growth conditions. Molecular and biochemical studies have been initiated to elucidate the biosynthetic pathway for the production of anatoxin-a, a neurotoxin produced exclusively in cyanobacteria. Polyketide synthases (PKS) are likely to be involved in this pathway as a correlation has been found between a specific PKS sequence and the production of anatoxin-a in PCC strains of the genus Oscillatoria. The determination of the entire gene cluster is in progress.



Publications 2006 of the unit on Pasteur's references database

Activity Reports 2006 - Institut Pasteur
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