Variations in the Microcystin Production of Planktothrix rubescens (Cyanobacteria) Assessed from a Four-Year Survey of Lac du Bourget (France) and from Laboratory Experiments

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 microg 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-PO4 (3-) 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.

Quantitative PCR Enumeration of Total/Toxic Planktothrix rubescens and Total Cyanobacteria in Preserved DNA Isolated from Lake Sediments

“…For Lake Bourget, the proliferation of MC-producing P. rubescens has been reported previously (7,24); the dominance of this taxon in Lake Bourget has been known at least since 1996 and is associated mainly with the process of restoring this ecosystem. In Lake Annecy sediments, no Planktothrix spp.…”

“…Proliferation of toxic cyanobacteria in aquatic ecosystems has been associated with major ecological disturbances, such as a decrease in aquatic biodiversity, with potential consequences for the entire food web. The toxic potential of several genera of planktonic freshwater cyanobacteria producing microcystins (MCs), the most prevalent cyanobacterial hepatotoxins in freshwaters, may also represent a considerable health risk for both wild and domestic animals as well as for human beings (7). Toxic cyanobacteria can even occur in less eutrophic systems, such as deep mesotrophic lakes in the Alps (7,29).…”

“…The toxic potential of several genera of planktonic freshwater cyanobacteria producing microcystins (MCs), the most prevalent cyanobacterial hepatotoxins in freshwaters, may also represent a considerable health risk for both wild and domestic animals as well as for human beings (7). Toxic cyanobacteria can even occur in less eutrophic systems, such as deep mesotrophic lakes in the Alps (7,29). In the latter case, Planktothrix rubescens is currently the dominant species reported for the following European subalpine lakes: Zurich (Switzerland) (55,56), Garda (Italy) (48), Mondsee (Austria) (27), Nantua (France) (17), and Bourget (France) (23,24).…”

Cyanobacterial dynamics and toxins concentrations in Lake Alto Flumendosa, Sardinia, Italy

“…We tested whether CB abundance could be a good proxy for MC concentration in the lake, as it has been shown by many studies on Planktothrix (Briand et al, 2005;Catherine et al, 2008;Dolman et al, 2012;Salmaso et al, 2014). A prerequisite for this relationship to be significant is the presence of a single dominant species (Salmaso et al, 2014).…”

Risk Assessment of Cyanobacteria and Cyanotoxins, the Particularities and Challenges of Planktothrix spp. Monitoring

“…Therefore P. agardhii grows well in the upper part of the water column of shallow eutrophic lakes, however it can also grow at several depths along the water column (Halstvedt et al, 2007). On the other hand, P. rubescens is well adapted in forming metalimnic populations of deep stratified lakes in spring and summer and when the lake loses its thermal stratification in the winter, it can be dispersed through the entire water column (Bright & Walsby, 2000;Briand et al, 2005). Planktothrix also has different water temperature tolerances when compared to other cyanobateria, making them organisms that can be easily found in subalpine lakes or in temperate regions during winter, so Planktothrix blooms may persist all year around and not only during summer or spring where temperatures and light irradiance are higher.…”