Fate of green plastids in Dinophysis caudata following ingestion of the benthic ciliate Mesodinium coatsi: Ultrastructure and psbA gene

• Dinophysis caudata ingested the benthic ciliate Mesodinium coatsi having plastids of Chroomonas sp.
• D. caudata quickly digested plastids of Chroomonas sp. after feeding on M. coatsi.
• D. caudata was able to repair photodamaged plastids after feeding on M. coatsi and Mesodinium rubrum.
• D. caudata has both phototrophic and heterotrophic nutrition.

Phototrophic Dinophysis species are known to acquire plastids of the cryptophyte Teleaulax amphioxeia through feeding on the ciliate Mesodinium rubrum or M. cf. rubrum. In addition, several molecular studies have detected plastid encoding genes of various algal taxa within field populations of Dinophysis species. The trophic pathway by which Dinophysis species acquire plastids from algae other than the cryptophyte genus Teleaulax, however, is unknown. In this study, we examined the fate of prey organelles and plastid genes obtained by Dinophysis caudata through ingestion of Mesodinium coatsi, a benthic ciliate that retains green plastids of Chroomonas sp. Transmission electron microscopy and molecular analysis revealed relatively rapid digestion of prey-derived plastids. Following digestion of M. coatsi, however, photodamaged D. caudata cells having olive-green rather than reddish-brown plastids were able to recover some of their original reddish-brown pigmentation. Results further suggest that plastid genes of various algal taxa detected in field populations of Dinophysis species may reflect prey diversity rather than sequestration of multiple plastid types. Ingestion and digestion of prey other than M. rubrum or M. cf. rubrum may also provide nutritional requirements needed to repair and perhaps maintain sequestered T. amphioxeia plastids.