Analysis of rRNA gene content in the Mediterranean dinoflagellate Alexandrium catenella and Alexandrium taylori: implications for the quantitative real-time PCR-based monitoring methods

A number of species belonging to the genus Alexandrium are among the main toxic microalgae responsible for Harmful Algal Blooms (HABs). The monitoring of coastal waters for the presence of these microalgae is essential to identify correlations between cell abundances and environmental factors that regulate bloom dynamics. In the attempt to improve the monitoring sensitivity and the rapidity at which a large number of field samples can be processed, several molecular methods for the detection of genetically distinct HAB species have been developed during the last years. In particular, real-time PCR has been shown to be a powerful method for quantitative detection of HAB species in environmental samples. When a plasmid is used as a standard, the knowledge of the amount of target gene per cell is essential for the determination of the cell number in the field sample. In this study, we analyzed the rRNA gene content variability in several Alexandrium catenella and Alexandrium taylori strains isolated from the Mediterranean Sea using a real-time PCR-based approach. The rRNA gene content was also analyzed in different growth phases, from early exponential to stationary conditions. The results showed a general variability in the rRNA gene content depending on the strain and, for the species A. taylori, in relation also to the growth phase. These results should be taken into account for the application of the real-time quantitative PCR-based techniques for monitoring purposes in coastal seawaters.