Validation of the detection of Alexandrium spp using specific RNA probes tested in a microarray format: Calibration of signal using variability of RNA content with environmental conditions

The dinoflagellate genus Alexandrium contains several toxin producing species and strains, which can cause major economic losses to the shell fish industry. It is therefore important to be able to detect these toxin producers and also distinguish toxic strains from some of the morphologically identical non-toxic strains. To facilitate this DNA probes to be used in a microarray format were designed in silico or developed from existing published probes. These probes targeted either the 18S or 28S ribosomal ribonucleic acid (rRNA) gene in Alexandrium tamarense Group I, Group III and Group IV, Alexandrium ostenfeldii and Alexandrium minutum. Three strains of A. tamarense Group I, A. tamarense Group III, A. minutum and two strains of A. ostenfeldii 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 ribonucleic acid (RNA) concentration or growth rate. The aim of this experiment was the calibration of several species-specific probes for the quantification of the toxic Alexandrium strains. Growth rates were highly variable but only elevated or lowered salinity significantly lowered growth rate for A. tamarense Group I and Group III; differences in RNA content were not significant for the majority of the treatments. Only light intensity seemed to affect significantly the RNA content in A. tamarense Group I and Group III, but this was still within the same range as for the other treatments meaning that a back calibration from RNA to cell numbers was possible. The designed probes allow the production of quantitative information for Alexandrium species for the microarray chip

Preliminary results of the MIDTAL project: a microarray chip to monitor toxic dinoflagellates in the Orkney Islands, U.K.

Harmful algae can cause economic damage to fisheries and tourism. Additionally, toxins produced by harmful algae and ingested via contaminated shellfish can be potentially fatal to humans. Monitoring these harmful algae can be difficult as determining cell morphology by light microscopy may be insufficient to give definitive species attribution. The goal of the EU FP7 project MIDTAL (microarrays for the detection of toxic algae) was to achieve rapid species identification using species specific probes for rRNA genes in a microarray chip format. Field samples from the Orkney Islands, an area of the U.K. that has a number of nuisance and toxic species were tested with the second generation of the microarray chip. Species specific probes were looked at for the toxin producing dinoflagellates Alexandrium tamarense Group III (North American clade) and Dinophysis acuta and also general class probes for Dinophyta, Heterokontaphyta and Prymnesiophyta over the course of a year. These were compared with light microscopy cell counts. A good agreement in determining presence and absence between the methods was found. The second generation microarray is potentially more sensitive than cell counts. However, further work is needed to ensure that the microarray signal for each species provides an accurate quantitative assessment

Distribution, occurrence and biotoxin composition of the main

En prens

Field testing for toxic algae with a microarray: initial results from the MIDTAL project

One of the key tasks in MIDTAL (MIcroarrays for the Detection of Toxic ALgae) is to demonstrate the applicability of microarrays to monitor harmful algae across a broad range of ecological niches and toxic species responsible for harmful algal events. Water samples are collected from a series of sites used in national phytoplankton and biotoxin monitoring across Europe. The samples are filtered; rRNA is extracted, labelled with a fluorescent dye and applied to a microarray chip. The signal intensity from >120 probes previously spotted on the chip is measured and analysed. Preliminary results comparing microarray signal intensities with actual field counts are presented.Versión del edito