Identification of Alexandrium (Dinophyceae) species using PCR and rDNA-targeted probes

A PCR (polymerase chain reaction)-based assay for the detection of Alexandr ium species in cultured samples using rDNA-targeted probes was developed. T he internal transcribed spacers 1 and 2 (ITS1 and ITS2) and the 5.8S riboso mal RNA gene (rDNA) from cultured isolates of A. tamarense (Lebour) Taylor, A. catenella (Whedon et Kofoid) Balech, A. fundyense Balech and A. lusitan icum Balech were amplified using PCR and sequenced. Sequence comparisons sh owed that the 5.8S and ITS1-ITS2 regions contain sequences specific for the Alexandrium genus, especially at the 3' end of the 5.8S coding region. PCR primers and a radioactive P-32-labeled DNA probe were devised for this reg ion. The crossreactivity of the PCR primers and probe was tested against cu ltured isolates of Alexandrium and other dinoflagellates and diatoms. All t he Alexandrium isolates screened reacted toward the genus-specific probe; i n contrast, the other groups of microalgae (dinoflagellates and diatoms) di d not react with the probe. Furthermore, the PCR amplification technique co mbined with the use of the rDNA-target probe allowed us to develop a method for the detection of Alexandrium cells in cultured samples. This PCR metho d might offer a new approach for the identification and enumeration of the HAB (harmful algal bloom) species present in natural phytoplankton populati ons.