Detection of Heterosigma akashiwo (Hada) using specific RNA probes: Variability of RNA content with environmental conditions

The raphidophyte Heterosigma akashiwo, which forms toxic blooms, causes major economical losses to the fish industry because of the fish kills involved. It is therefore important to be able to detect not only H. akashiwo but other toxic phytoplankton species as well, rapidly and accurately to reduce losses by fish kills. With this purpose, DNA sequences from H. akashiwo 18S and 28S rRNA gene regions were studied in silico to design species-specific probes to be used in a microarray format. Three strains of H. akashiwo (AC 265, AC 266 and GUMACC 120) were grown at optimal conditions and transferred into new environmental conditions changing either the light intensity, salinity, temperature or nutrient concentrations, to check if any of these environmental conditions induced changes in the cellular RNA concentration. The aim of this experiment was the calibration of several species-specific probes for the quantification of H. akashiwo. Differences on RNA content were not significant (p < 0.05) in any of the treatments, therefore the calibration curves were validated. The designed probes are reliable for the detection and quantification of H. akashiwo cells in natural waters.