Alexandrium minutum strains from a recombinant cross show correlated allelopathic activity against the diatom Chaetoceros muelleri and the parasite Amoebophrya sp., independent of PST toxicity.

Abstract

Dinoflagellates of the genus Alexandrium can produce bioactive extracellular compounds (BECs) responsible for a wide range of effects on many organisms. These compounds are poorly characterized within the genus Alexandrium. The transmission of the allelopathic phenotype within the recombinant progeny in dinoflagellates has not been documented either. This study investigated the effects of these allelochemicals produced by two parental strains of the dinoflagellate Alexandrium minutum and their 14 recombinant progeny against two targets, the diatom Chaetoceros muelleri and the dinoflagellate parasite Amoebophrya sp.. Analyses by flow cytometry on proxy parameters of cell physiology revealed that the allelochemicals produced by 15 out of 16 strains appear to induce deleterious effects on the photosynthetic apparatus of C. muelleri as well as on cell size. The cell membranes of C. muelleri were also damaged by the filtrate of 9 strains. Finally, the allelochemicals of 8 A. minutum strains seem to have a deleterious effect on the cell membranes of Amoebophrya sp. dinospore. The deleterious effects against the two targets were correlated. However, they were not correlated with pH, cell size, or paralytic shellfish toxin content. Overall, our results suggest that 1) among the allelochemicals produced by A. minutum, some would have an effect on the same molecular targets in both Amoebophrya sp. and in C. muelleri, 2) specific metabolite production of each strain was responsible for the range of effects observed and 3) the heritability of allelochemical production in A. minutum may involve several genetic loci.