CO₂‐CONCENTRATING MECHANISMS OF THE POTENTIALLY TOXIC DINOFLAGELLATE PROTOCERATIUM RETICULATUM (DINOPHYCEAE, GONYAULACALES)¹

Abstract

The low CO 2 concentration in seawater poses severe restrictions on photosynthesis, especially on those species with form II RUBISCO. We found that the potentially toxic dinoflagellate Protoceratium reticulatum Clap. et J. Lachm. possesses a form II RUBISCO. To cast some light on the mechanisms this organism undergoes to cope with low CO 2 availability, we compared cells grown at atmospheric (370 ppm) and high (5000 ppm) CO 2 concentrations, with respect to a number of physiological parameters related to dissolved inorganic carbon (DIC) acquisition and assimilation. The photosynthetic affinity for DIC was about one order of magnitude lower in cells cultivated at high [CO 2 ]. Endpoint pH-drift experiments suggest that P. reticulatum was not able to efficiently use HCO 3 ) under our growth conditions. Only internal carbonic anhydrase (CA) activity was detected, and its activity decreased by about 60% in cells cultured at high [CO 2 ]. Antibodies raised against a variety of algal CAs were used for Western blot analysis: P. reticulatum extracts only cross-reacted with anti-ß-CA sera, and the amount of immunoreactive protein decreased in cells grown at high [CO 2 ]. No pyrenoids were observed under all growth conditions. Our data indicate that P. reticulatum has an inducible carbonconcentrating mechanism (CCM) that operates in the absence of pyrenoids and with little intracellular CO 2 accumulation. Calculations on the impact of the CA activity to photosynthetic growth [CO 2 ] suggest that it is an essential component of the CCM of P. reticulatum and is necessary to sustain the photosynthetic rates observed at ambient CO 2 .

Differential effects of ocean acidification on growth and photosynthesis among phylotypes of Symbiodinium (Dinophyceae)

“…Marine dinoflagellates Prorocentrum minimum, Heterocapsa triquetra, Ceratium lineatum, and Protoceratium reticulatum all appear to regulate their CCM activity through differential expression of carbonic anhydrases (CAs) in response to changes in external CO 2 concentration (Rost et al 2006;Ratti et al 2007); such a capacity is clearly beneficial to tolerate large changes of pCO 2 , and hence pH in the case of these species, associated with dinoflagellate blooms (Rost et al 2006;Ratti et al 2007). Thus, a similar regulatory (buffering) mechanism could exist for phylotype A13.…”

Interactive effects of ocean acidification and nitrogen limitation on two bloom-forming dinoflagellate species

“…The majority of marine phytoplankton exhibit effective CCMs, which allow them to grow rather independently from CO 2 availability (e.g. Rost et al 2006, Fu et al 2007, Ratti et al 2007). This does not mean, however, that species do not benefit from increasing CO 2 concentrations.…”

Growth- and nutrient-dependent gene expression in the toxigenic marine dinoflagellate Alexandrium minutum

“…The typical dinoflagellate response to a reduced concentration of dissolved CO 2 is an increase in amount and per-cell-activity of the enzymes involved in the dehydration of HCO 3 , the extracellular and intracellular carbonic anhydrases (CAs) (Berman-Frank et al, 1994;Ratti et al, 2007). We identified an extracellular d-CA similar to that of the bloom-forming marine dinoflagellate Lingulodinium polyedrum see Toulza et al, 2010), as well as an intracellular CA, which were both significantly higher expressed in the stationary-phase control cultures than in the exponentially growing control (Supplementary Table 2).…”