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Monitoring toxigenic cyanobacteria in freshwaters is of great importance due to the adverse health impacts on humans and aquatic organisms. Here we studied cyanobacterial occurrence and biodiversity in a drinking water reservoir in Tehran province, Iran. In total, nine different species representing three orders of Synechococcales, Oscillatoriales and Nostocales were isolated and classified into six families and seven genera ranging from 92.3% to 99.0% similarities in their partial 16S rDNA with GenBank sequences. The cultures were analyzed for cyanotoxins production by the Artemia salina bioassay, ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and also screened for the presence of marker genes involved in toxins production. Ethyl acetate extracts of three strains showed more than 50% mortality on A. salina larvae after 24 h at a concentration of 500 µg/ml. Production of at least one of the cyanotoxins, microcystin (MC), cylindrospermopsin (CYN) and anatoxin-a (ATX-a), was detected in 6 of the strains. Seven MC variants with a total concentration of 130.6 ng/mg of biomass dry weight were detected for the strain Phormidium sp. UTMC6001 and molecular screening of the mcyE gene also confirmed the presence of this biomarker in its genome. Our study also revealed the production of CYN in a novel picocyanobacterial strain Cyanobium sp. UTMC6007 at 1.0 ng/mg of biomass dry weight. Considering the limited information on freshwater toxic cyanobacteria taxonomy in the Middle East, these findings will expand our knowledge and consequently aid in development of new water management policies in future.

The temporal variations in cyanobacteria and microcystin production in a tropical reservoir, Kranji Reservoir in Singapore, were studied from February 2008 to August 2009 by using molecular techniques and enzyme-linked immunosorbent assay (ELISA) respectively. Results from PCR and qPCR showed that Microcystis and Anabaena were present (mean concentrations 4.16 × 10 6 gene copies/mL and 4.47 × 10 4 gene copies/mL respectively) and were well correlated to each other ( P Microcystis was the primary microcystin producer. The average percentage of toxigenic Microcystis spp. was 55.92%, whereas no Anabaena -specific microcystin producing gene was detected. Microcystis -specific microcystin-producing genes mcyB and mcyD were detected in all the samples, together with dominant detection of mcyA and mcyE genes. However, a low positive detection rate was observed for mcyC . Due to the combined effects of high temperature, light and nutrient conditions in this tropical reservoir, the Microcystis cell concentrations were higher and more uniform compared to other Microcystis blooms reported in subtropical and temperate regions. Furthermore, the proportion of toxigenic Microcystis in the total Microcystis population was considerably higher. Principle component analysis and multiple linear regression analysis showed that total nitrogen and total phosphorus were positively correlated with the abundances of total Microcystis and toxigenic Microcystis . In addition, total nitrogen, pH and dissolved oxygen were positively correlated with the microcystin concentration.