INGESTION AND RETENTION OF CHROOMONAS SPP. (CRYPTOPHYCEAE) BY GYMNODINIUM ACIDOTUM (DINOPHYCEAE)¹

Abstract

Gymnodinium acidotum Nygaard, a blue‐green dinoflagellate previously shown to contain cryptophycean chloroplasts and other organelles, was observed from water and soil samples and in culture. The dinoflagellate excysts from soil samples as a mononucleated colorless cell that is positively phototactic. Colorless cells in unialgal culture remain colorless and can only be maintained less than one week whereas pigmented cells cultured unialgally grow for 10 days but then decline rapidly. Colorless cells cultured with Chroomonas spp. regain chloroplasts and have been maintained in mixed cultures for nine months. Fifty‐seven percent of the dinoflagellates from mixed cultures are bi‐nucleated, and three cells have been observed possibly ingesting cryptophytes. We suggest that cryptophycean chloroplasts are retained and possibly utilized by G. acidotum for at least ten days and then digested.

The extraordinary longevity of kleptoplasts derived from the Ross Sea haptophyte Phaeocystis antarctica within dinoflagellate host cells relates to the diminished role of the oxygen-evolving Photosystem II and to supplementary light harvesting by mycosporine-like amino acid/s

“…Kleptoplasty, the temporary retention of functional chloroplasts derived from algal prey, has been described for several heterotrophic dinoflagellates [3][4][5][6][7]. A novel and abundant dinoflagellate group, related to the icthyotoxic genera Karenia and Karlodinium, but without sharing evolutionary history with its plastids, was discovered by Gast et al [8] in the Ross Sea, Antarctica.…”

“…When deprived of P. antarctica cells, RSD gradually lose their kleptoplasts over a period of 5-8 months, or longer [9,10]. Other kleptoplastidic dinoflagellates generally need to acquire new plastids within 1 month, presumably because the acquired kleptoplasts do not maintain photosynthetic functionality over longer time periods [3,6,11]. On the other hand, chloroplasts sequestered within the sacoglossan sea slugs, are capable of photosynthesis for approximately 10-months in the absence of algal nuclei [12,13].…”

Morphological Transition in Kleptochloroplasts after Ingestion in the Dinoflagellates Amphidinium poecilochroum and Gymnodinium aeruginosum (Dinophyceae)

“…In fact, the cryptomonads that G. acidotum can ingest are members of the genus Chroomonas (which are blue-green) only, and no other cryptophytes, such as Cryptomonas, can be ingested (Fields and Rhodes 1991). It appears that the specificity of the dinoflagellate for its cryptomonad prey is stricter in freshwater dinoflagellates than it is in marine species.…”

“…Moreover, the division of the kleptochloroplast of the freshwater Gymnodinium is synchronised with the host cell division and each half of the kleptochloroplast is inherited by each daughter cell (Fields and Rhodes 1991;Schnepf et al 1989). Considering all above, the kleptochloroplasts in G. acidotum and G. aeruginosum represent a much more advanced stage of development of a true chloroplast from an endosymbiont than that seen in Amphidinium poecilochroum and A. latum (Fields and Rhodes 1991;Yamaguchi et al 2011).…”

“…However, it is unknown how and when organelles such as the ejectosomes are eliminated, and how the kleptochloroplasts are modified to become highly-lobed. Although previous studies revealed the general ultrastructure of the host and the kleptochloroplast (Fields and Rhodes 1991;Horiguchi and Pienaar 1992;Larsen 1988), few studies examine structural changes in the kleptochloroplasts over time, from ingestion to their disappearance.…”