Variations in the Microcystin Production of Planktothrix rubescens (Cyanobacteria) Assessed from a Four-Year Survey of Lac du Bourget (France) and from Laboratory Experiments |
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Authors: | J-F Briand S Jacquet C Flinois C Avois-Jacquet C Maisonnette B Leberre J-F Humbert |
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Institution: | (1) UMR CARRTEL, Station INRA d'Hydrobiologie Lacustre, Equipe de Microbiologie Aquatique, BP 511, 74203 Thonon-les-Bains Cedex, France;(2) Laboratoire des Sciences de l'Eau et de l'Environnement, Faculté des Sciences, 123 avenue A. Thomas, 87060 Limoges Cedex, France;(3) Laboratoire Environnement et Chimie Analytique, CNRS ERS 657, Ecole Supérieure de Physique et Chimie Industrielles, 10 rue Vauquelin, 75005 Paris, France |
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Abstract: | Between 1999 and 2002, a routine survey of water quality in the Lac du Bourget was performed to study the dynamics and microcystin
(MC) production of Planktothrix rubescens. Using liquid chromatography coupled to diode array detection and mass spectrometry, we found that two main variants (d-Asp3] and d-Asp3, Dhb7] microcystin-RR) were produced. The proportion of these two variants was not influenced by the depth or season of sampling.
Expressed in microcystin-LR equivalents, high microcystin concentrations were recorded from August to December each year,
reaching values of up to 6.7 μg L−1. A significant correlation was found between the microcystin cell content and the cell densities of P. rubescens. Cellular quotas of microcystins ranged from 0.1 to 0.3 pg cell−1. Simultaneously, laboratory experiments were performed on a strain of P. rubescens isolated from the lake to assess the potential impact of various P–PO43− concentrations on intra- and extracellular microcystin production. Unlike natural populations, this strain only produced
d-Asp3] MC-RR. The intracellular microcystin content was similarly correlated to the cell density, but the cellular quota was slightly
higher (0.3–0.7 pg cell−1) than in the natural population. Again, as in the natural population, a linear relationship was found between growth rate
and microcystin production rate. These findings support the hypothesis that environmental factors, such as phosphate concentrations,
have no direct impact on microcystin production by P. rubescens, but act indirectly by affecting growth rate. |
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