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This study is to develop and validate a real-time quantitative PCR (rt-QPCR) assay for rapid quantitation of microcystin-producing Microcystis using unprocessed surface water samples collected from Alberta lakes. Microcystin synthetase gene E (mcyE) was targeted for microcystin-producing Microcystis and 16S rRNA was used to measure blooming level of total cyanobacteria. The assay was optimized and validated with 20 reference samples collected in 2011. The limit of detection (LOD) of rt-QPCR was 50 copies/ml for both mcyE and 16S rRNA. An excellent precision was observed in 24 replicates [coefficient of variation (cv)=1.12% for 1.0E+05 and = 0.79% for 1.0E+03 copies]. The rt-QPCR assay was applied for detection of mcyE in 527 water samples collected from 45 lakes during the open-water season of 2012 in Alberta and 369 samples were mcyE positive. Microcystin-producing Microcystis was detected in 41 out of the 45 lakes in which, relatively high copy numbers of mcyE (≥ 1.0E+05 copies/ ml) were determined in 9 lakes. Cyanobacteria were present in all 45 lakes determined by 16S rRNA. The rt-QPCR assay developed with specific target to mcyE is sensitive, specific and robust for rapid detection and differentiation of toxic Microcystis from non-toxic cyanobacteria in surface water.

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