Abstract
The summer phytoplankton structure of ten Bulgarian waterbodies was studied by HPLC analysis of marker pigments, light microscopy (LM) and PCR amplification of mcyB and mcyE gene sequences. The aim was to detect biodiversity and spread of toxigenic strains of potential microcystin producers and the important bloom-forming genus Microcystis in particular. The screening was done in three waterbodies, where Microcystis had already been found (Lakes Ezerets and Durankulak and Reservoir Koprinka), three waterbodies from which it had not been reported (Reservoirs Shilkovtsi, Zhrebchevo, Suedinenie) and four reservoirs that were sampled for the first time (Malka Smolnitsa, Plachidol 2, Preselka, Duvanli). LM and HPLC data similarly showed that cyanoprokaryotes contributed significantly to the total phytoplankton composition (29%) and biomass (15–87%) in nine sampled waterbodies. Microcystis aeruginosa, M. natans, M. smithii, M. wesenbergii, Microcystis spp., M. cf. comperei and M. pseudofilamentosa, were identified using LM (the last two tropical species were found for the first time in the country). Despite the low contribution of Microcystis to the phytoplankton diversity (1–4 taxa per sample) and to the total phytoplankton biomass (< 0.01–0.5%), 57 toxigenic strains of this genus were revealed by PCR, most of which demonstrated high similarity with NCBI M. aeruginosa and M. wesenbergii strains.
Highlights
IntroductionScientific knowledge about Cyanoprokaryota/ Cyanobacteria ( known as blue-green algae) and environmental factors promoting their mass development (blooms), as well as their toxic metabolites (cyanotoxins) and primary toxin exposure vehicles (drinking water, recreational water activities, freshwater seafood) has rapidly advanced in recent times (Merel et al, 2013; Ibelings et al, 2014; Descy et al, 2016; Meriluoto et al, 2017; Flores et al, 2018)
Scientific knowledge about Cyanoprokaryota/ Cyanobacteria and environmental factors promoting their mass development, as well as their toxic metabolites and primary toxin exposure vehicles has rapidly advanced in recent times (Merel et al, 2013; Ibelings et al, 2014; Descy et al, 2016; Meriluoto et al, 2017; Flores et al, 2018)
The primary grouping was around the National Centre for Biotechnology Information (NCBI) strains of two Microcystis species – M. aeruginosa and M. wesenbergii (Fig. 11)
Summary
Scientific knowledge about Cyanoprokaryota/ Cyanobacteria ( known as blue-green algae) and environmental factors promoting their mass development (blooms), as well as their toxic metabolites (cyanotoxins) and primary toxin exposure vehicles (drinking water, recreational water activities, freshwater seafood) has rapidly advanced in recent times (Merel et al, 2013; Ibelings et al, 2014; Descy et al, 2016; Meriluoto et al, 2017; Flores et al, 2018). The most common and most frequently studied cyanotoxins are the cyclic heptapetides microcystins, which occur in about 280 variants and are produced by several cyanoprokaryote genera (Pelaez et al, 2010; Catherine et al, 2017; Meriluoto et al, 2017; Bouaicha et al, 2019; Le Manach et al, 2019; Svirčev et al, 2019; Massey et al, 2020; Stoyneva-Gärtner et al, 2021) One of these genera, Microcystis Kütz., is widely spread in the freshwater phytoplankton and contains more than 50 species (Komárek et al, 2014; Le Manach et al, 2019; Guiry & Guiry, 2021) described according to the rules of the International Code of Nomenclature for Algae, Uzunov B., Stefanova K., Radkova M., Descy J.-P., Gärtner G., Stoyneva-Gärtner M. There is accumulating evidence that an increase of nutrient concentrations and water temperature may promote the potentially toxic Microcystis genotypes (Vézie et al, 2002; Davis et al, 2009; Joung et al, 2011; Srivastava et al, 2015; Scherer et al, 2017; Jankowiak et al, 2019)
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