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Applied and Environmental Microbiology, June 2008, p. 3839-3848, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.02343-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Temporal Variations in the Dynamics of Potentially Microcystin-Producing Strains in a Bloom-Forming Planktothrix agardhii (Cyanobacterium) Population{triangledown} ,{dagger}

Enora Briand,1,2 Muriel Gugger,1,3 Jean-Christophe François,4,5,6 Cécile Bernard,1 Jean-François Humbert,3,7* and Catherine Quiblier1,8*

MNHN, USM505/EA4105 Ecosystèmes et Interactions Toxiques, 57 rue Cuvier, case 39, 75231 Paris Cedex 05, France,1 SCE, Département Eau, Pôle Fleuves, Rivières et Milieux Humides, Route de Gachet, 44307 Nantes, France,2 Institut Pasteur-CNRS URA 2172, Unité des Cyanobactéries, 25-28 rue du Dr Roux, 75015 Paris, France,3 INSERM, U565, Acides Nucléiques: Dynamique, Ciblage et Fonctions Biologiques, 57 rue Cuvier, CP26, F-75231 Paris Cedex 05, France,4 MNHN, USM503, Département de Régulations, Développement et Diversité Moléculaire, Laboratoire des Régulations et Dynamique des Génomes, 57 rue Cuvier, CP26, F-75231 Paris Cedex 05, France,5 CNRS, UMR5153, Acides Nucléiques: Dynamique, Ciblage et Fonctions Biologiques, 57 rue Cuvier, CP26, F-75231 Paris Cedex 05, France,6 INRA, UMR CARRTEL, BP 511, 74203 Thonon-les-Bains Cedex, France,7 Université Paris 7, 2 Place Jussieu, 75005 Paris, France8

Received 17 October 2007/ Accepted 18 April 2008

The concentration of microcystins (MCs) produced during blooms depends on variations in both the proportion of strains containing the genes involved in MC production and the MC cell quota (the ratio between the MC concentration and the density of cells with the mcyA genotype) for toxic strains. In order to assess the dynamics of MC-producing and non-MC-producing strains and to identify the impact of environmental factors on the relative proportions of these two subpopulations, we performed a 2-year survey of a perennial bloom of Planktothrix agardhii (cyanobacteria). Applying quantitative real-time PCR to the mcyA and phycocyanin genes, we found that the proportion of cells with the mcyA genotype varied considerably over time (ranging from 30 to 80% of the population). The changes in the proportion of cells with the mcyA genotype appeared to be inversely correlated to changes in the density of P. agardhii cells and also, to a lesser extent, to the availability of certain nutrients and the abundance of cladocerans. Among toxic cells, the MC cell quota varied throughout the survey. However, a negative correlation between the MC cell quota and the mcyA cell number during two short periods characterized by marked changes in the cyanobacterial biomass was found. Finally, only 54% of the variation in the MC concentrations measured in the lake can be explained by the dynamics of the density of cells with the MC producer genotype, suggesting that this measurement is not a satisfactory method for use in monitoring programs intended to predict the toxic risk associated with cyanobacterial proliferation.

* Corresponding author. Mailing address for Jean-François Humbert: INRA, UMR CARRTEL, BP 511, 74203 Thonon-les-Bains Cedex, France. Phone: 33 (0)4 50 26 78 09. Fax: 33 (0)4 50 26 07 60. E-mail: humbert{at}thonon.inra.fr. Mailing address for Catherine Quiblier: MNHN, USM505/EA4105 Ecosystèmes et Interactions Toxiques, 57 rue Cuvier, case 39, 75231 Paris Cedex 05, France. Phone: 33 (0)1 40 79 56 30. Fax: 33 (0)1 40 79 35 94. E-mail: quiblier{at}mnhn.fr

{triangledown} Published ahead of print on 25 April 2005.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, June 2008, p. 3839-3848, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.02343-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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