Evaluating the effectiveness of various biochemical and molecular techniques to assess microcystin risk during the onset process of Microcystis blooms (delay-development stages)

A variety of cyanotoxins (e.g., microcystin) threaten water safety globally, and biochemical methods and mo-lecular techniques have been used to assess microcystin risk. When a toxic bloom breaks out and associated microcystin risk will be changed, but whether these techniques is proper to assess microcystin risk for this process, remains unknown. Herein, the onset process (delay-development stages) of a bloom was simulated using a toxic strain of Microcystis aeruginosa-915, and the microcystin risk was assessed by biochemical techniques (ELISA and HPLC) and molecular techniques (DNA-and RNA-based qPCR). Results showed that indirect ELISA and HPLC could certify microcystin risk via accurate quantification of microcystin concentrations. Compared to indirect ELISA, direct ELISA underestimated microcystin risk due to a decrease of microcystin quantifications (20-55%) resulting from the competitive inhibition by elevated AOMs at development stage. Reliability of mcyD gene copies using DNA-based qPCR to indirectly assess microcystin risk was affected by microcystin-producing biomass at development stage. RNA-based qPCR could be a promising tool to achieve early-warning and real-time assessments of microcystin risk for this process. Besides, the ratio of mRNA/DNA copies of mcyD were proposed as an indicator, since it performed better (r = 0.93, p < 0.01) to indirectly assess microcystin risk than their total copies (r = 0.86, p < 0.01) for bloom samples. These results would provide a detailed guideline for water managers to employ proper techniques for assessments of microcystin risk during the onset process of a toxic bloom.

Automated summary

This study assessed the microcystin risk of a toxic bloom using biochemical and molecular techniques. The results showed that ELISA and HPLC can accurately quantify microcystin concentrations and assess the risk. However, direct ELISA underestimated the risk at the development stage, and the reliability of DNA-based qPCR was affected by biomass. RNA-based qPCR could be a promising tool for early-warning and real-time assessments of microcystin risk.