Abstract
The paper presents results from the first application of polyphasic approach in studies of field samples from Bulgaria. This approach, which combined the conventional light microscopy (LM) and molecular-genetic methods (based on PCR amplified fragments of microcystin synthetase gene mcyE), revealed that almost all microcystin-producers in the studied eutrophic waterbodies belong to the genus Microcystis. During the molecular identification of toxin-producing strains by use of HEPF × HEPR pair of primers, we obtained 57 sequences, 56 of which formed 28 strains of Microcystis, spread in six clusters of the phylogenetic tree. By LM, seven Microcystis morphospecies were identified (M. aeruginosa, M. botrys, M. flos-aquae, M. natans, M. novacekii, M. smithii, and M. wesenbergii). They showed significant morphological variability and contributed from <1% to 98% to the total biomass. All data support the earlier opinions that taxonomic revision of Microcystis is needed, proved the presence of toxigenic strains in M. aeruginosa and M. wesenbergii, and suppose their existence in M. natans. Our results demonstrated also that genetic sequencing, and the use of HEPF × HEPR pair in particular, can efficiently serve in water quality monitoring for identifying the potential risk from microcystins, even in cases of low amounts of Microcystis in the water.
Highlights
Some hazardous toxigenic species from the phylum Cyanoprokaryota/Cyanobacteria can form harmful algal blooms commonly abbreviated as CyanoHABs.The increasing and widespread concern regarding the serious threat which these algae and their toxins pose to human and animal health is consistent with the recent growth in interest on the topic [1]
Phytoplankton Species Composition Obtained by Light Microscopy (LM)
The lack of NODs in the checked water bodies (WBs) [4] is in accordance with the negative PCR signal for NOD-producing genes obtained in this study and the absence of its causative agents, Nodularia species [22], in the phytoplankton samples processed by light microscopy (LM)
Summary
Some hazardous toxigenic species from the phylum Cyanoprokaryota/Cyanobacteria (known as blue-green algae) can form harmful algal blooms commonly abbreviated as CyanoHABs. The increasing and widespread concern regarding the serious threat which these algae and their toxins (cyanotoxins) pose to human and animal health is consistent with the recent growth in interest on the topic [1]. 2000–2015, cyanoprokaryotic blooms were recorded in 14 WBs, and in 16 WBs cyanotoxins (mostly microcystins—MCs, and nodularins—NODs and saxitoxins—SXTs) were found [2,3]. From the samples with detected cyanotoxins in the period 2000–2015, 44 cyanoprokaryotes were determined by light microscopy (LM) [2]. It is widely known that the traditional LM identification of some bloom causative species remains problematic because of the unresolved taxonomy of certain cyanoprokaryote genera. The phenotypic flexibility of some standard diagnostic features in the taxonomy of cyanoprokaryotes—including the shape and structure of colonies, presence/absence of gas vesicles, akinetes, or heterocytes [5,6,7,8]—has promoted the parallel use of both morphological and molecular phylogenetic data in a common polyphasic approach [9,10,11]
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