Determination of toxic cyanobacteria and toxins in Lake Uluabat

In many parts of the world, especially in freshwaters, widespread cyanobacteria proliferation occurs due to global warming and antropogenic eutrophication. Cyanobacteria adversely affects aquatic ecosystems both by causing taste and odor problems in waters and with cyanotoxins they produce. The aim of this study was to investigate cyanotoxins and potentially toxic cyanobacteria in Lake Uluabat, an important ecological site for our country. Water column and plankton tow samples were collected from four different sites between June and September of 2015 and 2016. Cyanobacterial strains isolated from Uluabat Lake were cultured. The presence of cyanobacterial toxins microcystin, saxitoxin, anatoxin-a and cylindrospermopsin in both field samples and culture samples were investigated by enzyme-linked immunosorbent assay (ELISA) and receptor-binding assay (RBA). On the other hand, 16S rRNA and toxin genes were screened by polymerase chain reaction (PCR) in these samples. Morphological characterizations suggested that the isolated strains belonged to Microcystis aeruginosa, Dolichospermum cf. sigmoideum, Limnothrix planctonica, Cuspidothrix issatschenkoi, Calothrix elenkinii, Planktothrix isothrix, Dolichospermum ellipsoides, Sphaerospermopsis aphanizomenoides, Synechocystis aquatilis, Aphanocapsa grevillei and Microcystis smithii. In addition, neighbor-joining (NJ) and maximum likelihood (ML) phylogenetic trees based on 16S rRNA gene sequences confirmed that nine strains belonged to M. aeruginosa, Limnothrix sp., Calothrix sp., S. aphanizomenoides and C. issatschenkoi. Mcy genes and microcystin production was determined in Lake Uluabat and M. aeruginosa (Aquameb 24 and 25) strains isolated from the lake. Total MC determined in Aquameb 24 strain was 430 µg g-1 dry weight, in plankton tow samples of 22.07.2015 Site 1 was 75 µg g-1 dry weight as determined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. In addition, mcyA and mcyB genes were detected in M. smithii and A. grevillei strains. In the phylogenetic trees, the mcyA sequences cloned from plankton tow samples were grouped together with those from M. aeruginosa strains in the world. Molecular and toxin data suggest that M. aeruginosa is the main species that contributes to the production of microcystins in Lake Uluabat. However, other Microcystis species or other genera may be producing microcystins as suggested by MC variants in the lake samples. This study is important in terms of providing information about microcystin and its producers in Lake Uluabat.