Combining Imaging Flow Cytometry and Molecular Biological Methods to Reveal Presence of Potentially Toxic Algae at the Ural River in Kazakhstan

Algal blooms occur in freshwater bodies throughout the world, often leading to fish kills. Cases of these kills along Ural River were reported 2018–2019, involving significant amount sturgeon farming areas. In this study, analysis algal samples from delta up 100 km inland was carried out August December 2019 using imaging flow cytometry (IFC), molecular biological, and microscopic techniques. We identified filamentous cyanobacteria Cuspidothrix issatschenkoi , Dolichospermum cf. flos-aquae macrosporum Pseudanabaena limnetica Planktothrix spp. as dominant potentially toxic phytoplankton species, we also found minor quantities Cylindrospermopsis raciborskii . For first time, phylogenetic investigations field clones establish taxa species identify presence genes encoding toxins. The complementary with nanopore-based next-generation sequencing overlapped results IFC instrumental revealing taxa. Real-time PCR indicated Microcystis ADA-clade well associated production microcystin ( mcyE ) neurotoxin saxitoxin sxtA originating cyanobacteria. These findings suggest that toxin-producing could become a threat near Atyrau, which can significantly affect aquaculture region.