First Observation of Microcystins in Tunisian inland waters: a threat to river mouths and lagoon ecosystems

1 - Microcystin pollution is known to affect different types of inland water bodies: river mouths and coastal lagoons may be affected by local production as well as by transportation through the freshwater network. Physicochemical and biological water quality, including the total microcystin concentration, was investigated from July to December 2003 in the reservoir Hjar, Tunisia. 2 - Microcystin levels and characterization of the different microcystin variants present were measured by protein phosphatase inhibition assays (PP2A) and by high performance liquid chromatography coupled to diode array detector and tandem mass spectrometry, respectively. The microscopic examination of the phytoplankton samples showed the dominance of the Oscillatoria and Pseudoanabaena genera. The total (particulate and dissolved) microcystin concentrations in the reservoir water varied between 23.4 and 7455.2 ng/l microcystin-LR equivalent per liter. 3 - The highest MCYST concentration was observed in November 2003. The analysis of the field bloom extract from this month by HPLC coupled to photodiode-array detector revealed the presence of five peaks having characteristic spectra of microcystins with a maximum of absorbance at 238 nm. HPLC/MS/MS analysis of this sample demonstrated the presence of three variants of microcystins: microcystin-LR (MCYST-LR), microcystin- (MCYST-RR), microcystin- (MCYST-YR). Therefore, estuaries of rivers contaminated by cyanobacteria toxins may play an important role on the transfer of these cyanotoxins through food chains

Unusual cohabitation and competition between Planktothrix rubescens and Microcystis sp. (cyanobacteria) in a subtropical reservoir (Hammam Debagh) located in Algeria

International audienceSuccession in bloom-forming cyanobacteria belonging to distant functional groups in freshwater ecosystems is currently an undescribed phenomenon. However in the Hammam Debagh reservoir (Algeria), P. rubescens and Microcystis sp. co-occur and sometimes proliferate. With the aim of identifying the main factors and processes involved in this unusual cohabitation, water samples were collected monthly from February 2013 to June 2015 at the subsurface at four sampling stations and along the entire water column at one sampling station. In addition, the composition of the cyanobacterial communities was estimated by Illumina sequencing of a 16S rRNA gene fragment from samples collected over one year (October 2013-November 2014). This molecular approach showed that the Hammam Debagh reservoir displays high species richness (89 species) but very low diversity due to the high dominance of Microcystis in this community. Furthermore, it appears that Planktothrix rubescens and Microcystis sp. coexisted (from September to January) but proliferated alternately (Spring 2015 for P. rubescens and Spring 2014 and Autumn 2014/2015 for Microcystis). The main factors and processes explaining these changes in bloom-forming species seem to be related to the variation in the depth of the lake during the mixing period and to the water temperatures during the winter prior to the bloom season in spring