MOLECULAR TYPING OF THE RED-TIDE DINOFLAGELLATE GONYAULAX-POLYEDRA INPHYTOPLANKTON SUSPENSIONS

A group of closely related DNA sequences each approx. 240 base pairs l ong ('Gp240 family') was detected in the DNA extracted from cultured c ells of the red-tide dinoflagellate Gonyaulax polyedra using the polym erase chain reaction. While members of the Gp240 family appeared to be present in the DNA of all the isolates of G. polyedra tested, no rela ted sequence could be detected in the DNA of other dinoflagellates, di atoms or marine bacteria. In a further set of experiments, the PCR sys tem based on the Gp240 DNA was used to probe phytoplankton samples col lected in the Northern Adriatic Sea during a red tide caused by G. pol yedra. The results showed that the members of the Gp240 family contain a short simple-sequence stretch giving rise to length polymorphism. T he potential of this molecular identification system to track G. polye dra in its natural environment is discussed. Considerations are also m ade on the evolution of the simple-sequence loci in marine organisms.