|Director : TANDEAU de MARSAC Nicole (firstname.lastname@example.org)|
The cyanobacteria share with plants the capacity to perform oxygenic photosynthesis by using light and water for the reduction of CO2. Endowed with capacities of acclimation to a wide range of environmental conditions, including extreme ones, they colonize most aquatic and terrestrial ecosystems. Some of them produce hepatotoxins or neurotoxins harmful to animals and Man. Research work in the Unit is focussed on the development and valorisation of the collection of cyanobacteria (PCC), in particular strains potentially toxic, and on the study of the molecular mechanisms controlling the acclimation of these micro-organisms to changes in environmental parameters.
1. The PCC "Pasteur "Pasteur Culture Collection of Cyanobacteria", centre of research and documentation on cyanobacteria (R. Rippka, M. Herdman and I. Iteman)
Our Unit possesses the largest collection of cyanobacteria in the world by the number of strains in pure cultures and by the diversity of their geographical origin and properties.
The PCC has several missions:
In collaboration with J.M. Delattre (Department of Waters and Environment, IP-Lille), expert tests have been set up for the identification and the determination of hepatotoxins in samples from surface waters.
Several databases are in constant evolution:
A second edition of the Bergey's Manual of Systematic Bacteriology has been published in 2001 in which the descriptions of the cyanobacterial strains are largely based on studies performed by our team on strains from the PCC.
2. Molecular mechanisms of the acclimation of cyanobacteria to the environment (N. Tandeau de Marsac)
Light and nutrients act in a number of circuits regulating cyanobacterial metabolism, and may, in some strains belonging to the genus Calothrix, control the differentiation of cells specialized for nitrogen fixation (heterocysts), and that of motile minifilaments (hormogonia), and/or regulate changes in pigment composition (complementary chromatic adaptation).
Cyanobacterial phytochromes, a family of photoreceptors ancestors of the plant phytochromes
Two cyanobacterial phytochromes, CphA and CphB, have been genetically characterized in Calothrix PCC 7601. These light-regulated histidine kinases act at an early step in the transmission of the red/far red light signal by a mechanism of phosphorylation/dephosphorylation of the response regulators RcpA and RcpB. In contrast to CphA that carries a covalently bound chromophore, CphB carries a non-covalently bound one. No cross talk has been detected between CphA-RcpA and CphB-RcpB, indicating that these couples are specific. Based on studies using a bacterial two-hybrid system, the RcpA protein forms homodimers. The 3D-structure of both RcpA and RcpB has been established. The biochemical and spectral properties of different mutants are being studied to elucidate the structure-function relationships of these four proteins (collaborations with W. Gärtner, Max Plank Institute, Mülheim der Rürh, Germany, and T. Hübschmann and T. Börner, Humboldt University, Germany, and with D. Ladant and G. Karimova, Unité de Biochimie Cellulaire, IP).
PII, a signal transducer that coordinates carbon and nitrogen metabolism
The primary structure of the PII (GlnB) protein is very conserved among prokaryotes and plants, its function, however, differs depending on organisms. In order to get deeper insights into the role of this protein in cell metabolism, different cyanobacteria are being studied. In the strains Synechococcus PCC 7942, obligate photoautotroph, and Synechocystis PCC 6803, facultative heterotroph, the phosphorylated form of PII inhibits the uptake of nitrate/nitrite ions. This inhibition is relieved when PII is liganded to 2-oxoglutarate and phosphorylated, i.e. in the presence of high carbon and low nitrogen concentrations. In Synechocystis, this modified form of PII inhibits the high affinity transport system for bicarbonate ions. Finally, the phosphorylation level of PII in both Synechococcus and Synechocystis depends on the intracellular redox potential and, consequently, the photosynthetic activity of the cell (collaboration with S. Bédu and R. Jeanjean, LCB, Marseille). This regulatory process allows cells to maintain a proper N/C balance in response to changes in light and nutrients (nitrogen and carbon) in the environment.
In the frame of a European Programme (PROMOLEC "Prochlorococcus molecular ecology", programme MAAST III, 1998-2001), some characteristics of Prochlorococcus marinus, a cyanobacterium extremely abundant in oligotrophic tropical and subtropical oceans, have been studied. This strain has the smallest cell size (diameter 0.5-0.6 mm), the smallest genome (1,67 Mb), the lowest G+C content (31 %) among cyanobacteria, and possesses atypical light harvesting antennae that consist of protein complexes containing divinyl-chlorophylls a and b but no phycobiliproteins.
P. marinus has a cyanobacterial-type PII that remains unphosphorylated, although its primary and quaternary structures are well-conserved (collaborations with S. Loiseaux-De Goër, CNRS, Roscoff, and A. Blondel, Unité de Biochimie cellulaire, IP). We have shown that P. marinus lacks the genetic information required for the assimilation of nitrate and nitrite ions. In spite of its lack of post-translational phosphorylation, the PII protein, however, might control the assimilation of the bicarbonate ions in response to changes in the intracellular concentration of 2-oxoglutarate (collaboration with S. Bédu, LCB-CNRS, Marseille).
3. Cyanobacterial genomes (N. Tandeau de Marsac)
In silico analyses of the sequence of the Synechocystis PCC 6803 genome revealed the presence of repeated motifs whose functions remain to be elucidated (collaboration with M. F. Sago, Service d'Informatique Scientifique, IP, and H. Geiselmann, Université J. Fourier, Grenoble). CyanoList, a genome browser for Synechocystis PCC6803, with the same Web server structure as SubtiList, has been created (collaboration with I. Moszer, Unité de Génétique des Génomes Bactériens).
Our team participates in a project on the sequencing of the genome of P. marinus SS120 (collaboration with the Génoscope, Evry).
In situ hybridizations (FISH) of potentially hepatotoxic cyanobacteria belonging to the genus Microcystis (green) and of eukaryotic organisms (amoebae; red) from a water sample. Detection with two different fluorochromes coupled to tyramide and observation under confocal laser scanning microscopy (W. Shönhuber and M. Herdman).
|More informations on our web site|
|Publications of the unit on Pasteur's references database|
|Office staff||Researchers||Scientific trainees||Other personnel|
LEFEBVRE Jacqueline (email@example.com)
HERDMAN Michael, CNRS (CR2, firstname.lastname@example.org)
ITEMAN Isabelle, IP (CR, email@example.com)
RIPPKA-HERDMAN Rosmarie, IP (CR, firstname.lastname@example.org)
ARAOZ Romulo, Postdoctoral Researcher
BEST Jennifer, Postdoctoral Researcher
COMTE Katia, Postdoctoral Researcher
LALOUI Wassila, Postdoctoral Researcher
LE ROCH Albane, DESS student
MARCEL Anne, DESS student
MLOUKA Alyssa, PhD student
WU Tianfu, Postdoctoral Researcher
CASTETS Anne-Marie, CNRS (AI, email@example.com)
COURSIN Thérèse, IP (TSL, firstname.lastname@example.org)
LAURENT Thierry, IP (TL, email@example.com)