SEDIMENTARY IMPRINT OF MICROCYSTIS AERUGINOSA (CYANOBACTERIA) BLOOMS IN GRANGENT RESERVOIR (LOIRE, FRANCE)¹

Abstract

Analysis of a sediment core taken from the Grangent reservoir in 2004 showed the presence of high concentrations of Microcystis aeruginosa Kütz. colonies at the sediment surface (250 colonies AE mL sediment )1 ) and also at depths of 25-35 cm (2300 colonies AE mL sediment )1 ) and 70 cm (600 colonies AE mL sediment )1 ). Measurements of radioactive isotopes ( 7 Be, 137 Cs, and 241 Am) along with photographic analysis of the core were used to date the deep layers: the layer located at )30 cm dates from summer 2003, and that located at )70 cm from 1990 to 1991. The physiological and morphological conditions of those benthic colonies were compared with those of planktonic colonies using several techniques (environmental scanning electron microscopy [ESEM], TEM, DNA markers, cellular esterases, and toxins). The ESEM observations showed that, as these colonies age, peripheral cells disappear, with no cells remaining in the mucilage of the deepest colonies (70 cm), an indication of the survival thresholds of these organisms. In the benthic phase, the physiological conditions (enzyme activity, cell division, and intracellular toxins) and ultrastructure (particularly the gas vesicles) of the cells surviving in the heart of the colony are comparable to those of the planktonic form, with all the potential needed for growth. Maintaining cellular integrity requires a process that can provide sufficient energy and is expressed in the reduced, but still existing, enzymatic activity that we measured, which is equivalent to a quiescent state.

Analysis of intracellular and extracellular microcystin variants in sediments and pore waters by accelerated solvent extraction and high performance liquid chromatography-tandem mass spectrometry

“…However, only four variants of similar chemistry have been tested thus far [15][16][17][18] and laboratory and field studies suggest differences in the adsorption properties of different microcystins [3,19,20]. Furthermore, no method has yet demonstrated the recovery of microcystins from intact cyanobacterial cells in sediments despite increasing evidence of the significance of this microcystin pool [7][8][9][10][11][12][13][14].…”

“…These recoveries were comparable to those of extracellular microcystins. Considering the fact that intracellular toxins can deposit onto sediment [7][8][9][10], be produced by living cells within sediment [11][12][13], and persist within deep sediment [14], the efficacy of our ASE to recover intracellular cyanotoxins from sediment material is a major advantage compared to currently available methods [15][16][17].…”

“…Microcystins can subsequently deposit into surficial sediments by adsorption to particulates [4][5][6] and within intact cyanobacterial cells [7][8][9][10] that settle to the lake bottom. Intracellular microcystins have also been found in benthic cyanobacteria growing on the surface sediments of shallow lakes [11][12][13] as well as in viable cyanobacterial colonies from deep sediments [14]. These reports highlight the need for an extraction method capable of rupturing the cells within sediments to recover intracellular toxins in addition to extracellular microcystins adsorbed to particles or dissolved within sediment pore waters.…”

Spatiotemporal Variations in Microcystin Concentrations and in the Proportions of Microcystin-Producing Cells in Several Microcystis aeruginosa Populations

“…In the same way, high MC cellular quotas preceding blooms of Planktothrix and Microcystis have been reported in Dutch lakes (24,25), suggesting that high concentrations of MC in the early stages of a bloom could enhance growth efficiency or could act as a grazing deterrent. We can also assume that high cellular quotas during the early stages of the bloom are due to the recruitment of highly toxic cells, since high MC contents have been found in the benthic colonies in the Grangent Reservoir (30).…”

Vertical Heterogeneity of Genotypic Structure and Toxic Potential within Populations of the Harmful Cyanobacterium Microcystis aeruginosa

“…Rapid disruption (<1 min) of the colonial structure was produced by low-power ultrasonic vibration (20 kHz) [33,34]. Isolated cells of M. aeruginosa were then counted under a microscope (Carl Zeiss, Oberkochen, Germany) at ×400 magnification with a Thoma counting chamber.…”