Allelopathy modulates toxins profiles and high activation of caspase-3/7 in Gymnodinium catenatum

Allelopathy in phytoplankton species can modify the community structure by growth inhibition, organelle damage, cellular stress, metabolic modifications, and by inducing programmed cell death (PCD). In this study, the allelopathic responses of G. catenatum, a paralytic toxin harmful algal bloom (HAB) forming species, towards the raphidophyte C. marina var. marina and the dinoflagellate Gymnodinium impudicum were evaluated. Gymnodinium catenatum was cultivated during 72 h in mixed cultures with and without direct cell contact with C. marina and G. impudicum. Growth, cell morphology, toxin profile, and caspases 3/7 activity were registered. Growth of G. catenatum exposed to C. marina and G. impudicum with and without direct cell contact was significantly reduced, toxin content decreased, and caspases 3/7 activity increased. Changes in the toxin profile were also observed, in general, with a higher content of gonyautoxin-2,3 (GTX2, 3), decarbamoyl gonyautoxin-2,3 (dcGTX2,3) and B1 analogs. In all cases the highest response was observed in direct cell contact with C. marina. These results allow new insights of the allelopathic responses of G. catenatum towards co-occurring HAB species confirming growth limitation and evidencing metabolic changes in the toxin content, as well as the induction of PCD.