Dinophyceae use exudates as weapons against the parasite Amoebophrya sp. (Syndiniales)

Abstract

Parasites of the genus Amoebophrya sp. are important contributors to marine ecosystems and can be determining factors in the demise of blooms of Dinophyceae, including microalgae commonly responsible for toxic red tides. Yet they rarely lead to the total collapse of Dinophyceae blooms. The addition of resistant Dinophyceae (Alexandrium minutum or Scrippsiella donghaienis) or their exudate into a well-established host-parasite culture (Scrippsiella acuminata-Amoebophrya sp.) mitigated the success of the parasite and increased the survival of the sensitive host. Effect were mediated via water-borne molecules without the need of a physical contact. Severity of the anti-parasitic defenses fluctuated depending on the species, the strain and its concentration, but never totally prevented the parasite transmission. The survival time of Amoebophrya sp. free-living stages (dinospores) decreased in presence of A. minutum but not of S. donghaienis. The progeny drastically decreased with both species. Integrity of the membrane of dinospores was altered by A. minutum which provided a first indication on the mode of action of these anti-parasitic molecules. These results demonstrate that extracellular defenses are an effective strategy against parasites that does not only protect the resistant cells but also have the potential to affect the whole surrounding community.