A search for mixotrophy and mucus trap production in Alexandrium spp. and the dynamics of mucus trap formation in Alexandrium pseudogonyaulax.

Recently, a hitherto unknown feeding strategy, the toxic mucus trap, was discovered in the dinoflagellate Alexandrium pseudogonyaulax. In this study, over 40 strains of 8 different Alexandrium species (A. ostenfeldii, A. tamarense, A. catenella, A. taylorii, A. margalefii, A. hiranoi, A. insuetum and A. pseudogonyaulax) were screened for their ability to ingest prey and/or to form mucus traps. The mucus trap feeding strategy, where a mucus trap is towed by the longitudinal flagellum remains unique to A. pseudogonyaulax. In additional experiments, details of the trap were examined and quantified, such as speed and frequency of trap formation as well as what happens to the trap after the A. pseudogonyaulax cell detaches from it. The percentage of A. pseudogonyaulax cells producing a mucus trap and the number of prey cells caught increased with increasing prey concentration, whereas the physical size of the traps was independent of prey concentration. In one strain given an excess of prey, within 1h over 90% of individual A. pseudogonyaulax cells had formed a trap, each containing an average of 45 prey cells. Individual A. pseudogonyaulax cells steadily produced traps and up to 5 traps were produced by a single A. pseudogonyaulax cell after only 24h. The attachment of an A. pseudogonyaulax cell to the trap only ceased during, and just following, cell division. Prey cells were, to some extent, capable of escaping from the mucus trap, but the trap remained sticky and continued catching prey for up to 48h after the trap had been abandoned by the A. pseudogonyaulax cell. These results reveal that the effects of the mucus trap extend far beyond the removal of prey through ingestion, and the potential impact of this strategy on surrounding cells is high.