Rapid on-site multiplex assays for total and toxigenic Microcystis using real-time PCR with microwave cell disruption

Abstract

A quantitative real-time polymerase chain reaction (qPCR) is a robust means by which to monitor toxin-producing cyanobacteria. However, qPCR usually requires DNA extraction, which is a time-consuming, labor-intensive pretreatment. To be able to quickly determine the potential of cyanotoxin contamination in the field, a rapid pretreatment method for DNA extraction and a portable qPCR device are needed. In this study, we applied a microwave-based method for the qPCR pretreatment and a multicolor portable qPCR with UPL and TaqMan probes to quantify toxigenic and total Microcystis. The method was tested using laboratory cultures of toxigenic Microcystis aeruginosa PCC7820. The qPCR results showed the cycle thresholds value (Ct value) correlated well with cell numbers, with detection limit at about 1,000 cells/ml. This scheme was applied in 22 environmental samples from six drinking water reservoirs (DWRs) in Taiwan. Although the results for qPCR were about four times higher than those of microscopic observation, good correlation between qPCR and microscope methods were obtained (r-square: 0.79, P < 0.01). The ratios of toxigenic Microcystis to total Microcystis in two reservoirs, Sin-Shan Reservoir and Shih-men Reservoir, were less than 10%. In three other reservoirs, Ren-Yi-Tan Reservoir, Nan-Hua Reservoir and Bao-Shan Reservoir, much higher (>46.1%) ratios were obtained. The scheme may assist quick assessment of the risk associated with toxic cyanobacteria in DWRs.