Uptake of high molecular weight dextran by the dinoflagellate Alexandrium catenella

Abstract

Carbohydrate macromolecules (dextrans) labeled with fluorescein isothiocyanate (FITC) were taken up by the dlnoflagellate Aiexandriurn catenella at a substrate concentration of 5 nlg C 1-'. The FITC-labeled dextrans appeared in what resembled food vacuoles inside the dinoflagellate cells. Between 5 and 50% of the cells contained fluorescent green vacuoles. A. catenella took up dextrans of high nlolecular weight (2000 kDa) but did not show significant uptake of lower molecular weight (20 kDa) dextrans. The uptake of the 2000 kDa dextran was higher w~t h addition of hurnic substances to the growth medium and did not seem related to the presence of bacteria. Phagocytosis of fluorescent microspheres (0.36 pm) by A. catenella was also investigated. Although aggregation of fluorescent microspheres was observed in the sulcal reglon of the cells, no evidence was found of phagocytosis of bacterial-size prey by A. catenella. These observations show that A. catenella has the capacity to take up high molecular weight organlc molecules, perhaps by pinocytosis.

Spring bloom community change modifies carbon pathways and C : N : P : Chl <i>a</i> stoichiometry of coastal material fluxes

“…Dinoflagellates have been shown to possess compensatory strategies to compete with fast-growing phytoplankton groups, such as allelopathy, mixotrophy, and internal nutrient storages (Legrand and Carlsson, 1998;Collos et al, 2004;Tillmann et al, 2008). B. baltica has recently been confirmed to effectively suppress growth of co-occurring diatoms by excretion of allelochemicals (Suikkanen et al, 2011), and utilization of residual P has been suggested to facilitate sustained growth of B.baltica in the 2004 mesocosms (Kremp et al, 2008).…”

Dinoflagellate bloom formation in natural assemblages with diatoms: nutrient competition and growth strategies in Baltic spring phytoplankton

“…It is possible that the species, like other bloomforming dinoflagellates, possesses compensatory strategies such as mixotrophy or utilization of dissolved organic nutrients and internal nutrient storages (Legrand & Carlsson 1998, Dyhrman & Anderson 2003, Collos et al 2004. Also, the role of P and, accordingly, N:P ratios needs to be examined more thoroughly.…”

Cycling of biologically available nitrogen in riverine humic substances between marine bacteria, a heterotrophic nanoflagellate and a photosynthetic dinoflagellate

“…HMW polymeric compounds such as HS are too large to pass the cytoplasmic membrane (Payne 1980) and must be degraded enzymatically before uptake (Raven 1980), or taken up actively via pinocytosis, a mechanism in which the plasma membrane extends and forms a vesicle enclosing liquid containing the HMW compounds (Klut et al 1987); this mechanism has so far been very little studied and the importance of it for phytoplankton nutrition is virtually unknown. However, Legrand & Carlsson (1998) recently showed that the dinoflagellate Alexandrium catenella could take up large (2000 kDa) fluorescein isothiocyanate (F1TC)-labeled dextrans, presumably by pinocytosis.…”