DETECTION OF TOXIN-PRODUCING CYANOBACTERIA BY USE OF PARAMAGNETIC BEADS FOR CELL CONCENTRATION AND DNA PURIFICATION

Early detection of water blooms caused by potential toxin-producing cy anobacteria is important in environmental monitoring, We present a new nucleic acid-based method for detection of cyanobacteria in water tha t utilizes the same paramagnetic solid phase (beads) For both bacteria l cell concentration and subsequent DNA, purification, In the cell con centration step, the beads were attracted to a magnet after cell adsor ption (in an alcohol- and salt-containing solution), and the supernata nt was removed, For DNA purification, a buffer containing guanidine th iocyanate and Sarkosyl lysed time concentrated cells, The addition of alcohol precipitated the released DNA onto the same solid phase as was used for the cell concentration, Finally, to remove PCR inhibitors, t he DNA was washed twice in alcohol while bound to the beads, All of th e bead-DNA complex was used in the subsequent PCR amplification. The d etection limit, as measured by 16S rDNA PCR amplification, was 50 cell s in a O.5-ml water sample, which is considerably lower than the limit (500 cells/ml) of toxic cyanobacteria tolerated in drinking water (Ne w South Wales Blue-Green Algae Task Force, 1992). Testing of water fro m natural habitats showed a defection limit in the same range as that for the defined samples, The detection limits and the simplicity of th e method (paramagnetic beads san be handled in automated systems) sugg est that our method is suitable for routine environmental monitoring.