Molecular identification and toxicity effects of cyanobacteria species isolated from the Khoor-e-Khooran mangrove forest, Persian Gulf

The increasing incidence of the harmful cyanobacterial blooms in mangrove ecosystem is a potential threat for aquatic organisms and their consumers. In the present study, we have evaluated the biodiversity of cyanobacteria and monitored their cyanotoxins. We isolated 120 bacterial isolates using BG11 medium from water and sediment samples collected from 10 stations throughout of the Khoor-e-Khooran mangrove forest at august 2018. Biodiversity and distribution pattern based on morphological characteristics showed that 10 cyanobacterial genera were spread over the studied area. Phormidium, Oscillatoria, Spirulina and Nostoc genera were dominated with frequency percentages of 25%, 20%, 10%, and 10% respectively. Analysis of 16S rRNA sequences showed that the strains have high similarity with type strains in NCBI GenBank ranged from 98% to 100%. Phylogenetic analysis proposed the non-indigenous origin of Microcystis strains because of their phylogenetic divergence. We detected microcystin gene in Microcystis sp. strain KH 3, Microcystis sp. strain KH 4 and Microcystis sp. strain KH 11, while nodularin and cylindrospermopsin gene were not detected in all isolated cyanobacteria. The extracted metabolites from KH 3 and KH 4 strains showed cytotoxicity with LC50 of 139.3 and 225.8 µg/mL against Artemia salina respectively. Their LC50 were 231.3 and 211.2 µg/mL against shrimp larvae respectively. They inhibited the proliferation of HUVEC cell lines with IC50 of 11.13 and 13.29 µg/mL and HEPG2 with IC50 of 15.49 and 12.51 µg/mL, respectively. Our results represented diversity and distribution pattern of cyanobacteria and demonstrated the incidence of microcystin in the Khoor-e-Khooran mangrove forest.