Development of real-time PCR for quantification of Cylindrospermopsis raciborskii cells and potential cylindrospermopsin-producing genotypes in subtropicalreservoirs of southern China

Abstract

Cylindrospermopsin (CYN) is of great concern to human and animal health due to its potential toxicity. The cyanobacterium Cylindrospermopsis raciborskii is considered the most common cyanobacterial species that produces CYN. The discovery of the cyr gene cluster responsible for CYN biosynthesis allows us to develop molecular methods that detect and quantify potentially CYN-producing C. raciborskii. This paper describes the development of real-time PCR (qPCR) assays capable of quantifying the total and CYN-producing C. raciborskii in subtropical reservoirs of southern China. We designed primers and probes specifically targeting the rpoC1 and cyrJ genes of C. raciborskii, and enabling quantification of its total cell numbers and potentially toxic genotypes, respectively. The qPCR showed strong linearity between 102 and 106 copies per reaction for both genes. This molecular method was validated against microscopic counting and a high correlation was found between them for quantifying C. raciborskii cell numbers in cyanobacterial cultures and water samples. Using qPCR, we detected potentially CYN-producing C. raciborskii in 34 of the 46 subtropical reservoirs of southern China, with the cyrJ/rpoC1 proportion ranging from 0.3 to 34.7%. CYN concentrations significantly correlated with both the copy numbers of cyrJ gene and the proportion of toxic C. raciborskii. Thus, the present real-time PCR method provides a reliable and faster method for estimating the potential toxicity of C. raciborskii blooms in this region. The wide distribution of potential CYN-producing C. raciborskii in the investigated subtropical reservoirs highlights the need for further monitoring.