## 4 Discussion
Considering _Microystis_ in particular, both LM and molecular-genetic approaches demonstrated its presence with uneven distribution of species and toxicen strains in eight of the ten studied sites (except in the mentioned above reservoirs Krapets and Kriva Reka). The results indicated low taxonomic (2 species; Table 2, Figure 5) but high genetic diversity (Figures 7 and 8). Most strains (81) were identified according to their homology with _mcyE_-based sequences and grouped in four clusters (Figure 7), and five strains homologous with _mcyB_ were spread in two clusters (Figure 8). Despite the high homology (100%) of more than 50% of the obtained sequences, only eleven (15%) of them were affiliated to the NCBI strains of both distinct species _M. aeruginosa_ and _M. wesenbergii_. For seven more strains we assume belonging to _M. wesenbergii_ based on our former polyphasic study and relevant sequences provided to NCBI [9] (Figure 7). In the same study the reasons for the low number of certain affiliations were discussed in detail, stressing that many NCBI strains are not supplied with relevant morphological descriptions, and that the value of some phylogenetic constructions is reduced because of using sequences from strains which have not passed taxonomic revision and therefore have incorrect or arbitrary names [9; 62]. Here we shall note also that many NCBI strains have only generic names, which obviously complicates the affiliation to distinct species. The phylogenetic trees, constructed from the analyzed _mcyE_ and _mcyB_ sequences and their homologous representatives from NCBI (Figures 7 and 8), demonstrated the complexity of the isolated sequences pool. This complexity reflects the relevant rich biodiversity of _Microystis_ strains in the studied waterbodies and is on accordance with our previous _mcyE_-based data, obtained from the same wetlands [9]. With this study we demonstrate for second time the presence of _mcy_ genes in the strains of _M. wesenbergii_ from Bulgaria. The potential toxicity of this species has long been debated (for details see [9; 19; 62]). The _mcyE_ toxicen sequences allied to this species were found for first time in the reservoirs Poroy and Izvornik 2, and were confirmed for the reservoir Sinyata Reka. Thus, considering our former data [9], MC-producing strains of _M. wesenbergii_ were found altogether in four Bulgarian waterbodies, where the species was also detected by LM observations at: Sinyata Reka, Vaya, Izvornik 2 and Poroy. The rare initial colonies of the species seen by LM in the samples from Poroy in August 2019 (Figure 5d) coincide with the undetectable amounts of MCs in this reservoir (Table 3). Our results on _mcyE_ sequences, LM observations and toxin analyses are consistent with the findings of _mcyE_ genes in a single strain of _M. wesenbergii_ isolated from Tasksi Lake (Turkey), which demonstrates MC production [63]. They coincide also with the records of _mcy_ genes A and B in M. _wesenbergii_[64], with detected MC production of its different strains [65] and its findings in field samples containing MCs (for details see [19; 62; 66]). Considering that the _mcyE_ gene has been successfully used to reveal the presence of potential MC-producing genera other than _Microystis_[2; 3; 6; 13; 14; 15; 16; 17; 63] and that species of such genera (e.g., _Anabaena_, _Dolichospermum_, _Spharospermopsis_, _Oscillatoria_, _Planktonrix_, _Raphidiopsis_ and _Aphanizomenon_ s.l.) were identified by conventional LM in the phytoplankton of the studied waterbodies (in some of which they dominated or were abundant), we can argue that in the processed samples MC-producing strains of all these genera were not found by molecular-genetic methods. The appearance of _Raphidiopsis ridorskii_ strain NCBI:toid2217671 (provided as _Cylindrospermopsis raciborskii_ Tau-Mac 1414 in NCBI and in Cluster IV on Figure 7) also does not show the occurrence of MC-producing strains of this species in our waterbodies due to its low similarity with the newly obtained sequence ManE3 (MW187820). Moreover, _R.