Bicarbonate Utilization by Marine Phytoplankton Species

Abstract

The contribution of bicarbonate to total dissolved inorganic carbon (DIC) utilization was investigated using 18 marine phytoplankton species, including members of Bacillariophyceae, Dinophyceae, Pqmnesiophyceae, and Raphidophyceae, was assayed as an indicator of extracellular GI-catalyzed HC@ utilization. For some species, extracellular CA was constitutive, in others activity was detected under conditions of carbon limitation, and in others, even under carbon-limited conditions, activity was not detected. I n species without extracellular CA, direct HC@ uptake was investigated using a pH dnji technique in a closed system, DIC measurements, and the use of the anion exchange inhibitor 4'4'-diisothiocyanatostilbene-2,2-disulfonic acid (DLDS) . Three of these species (Chaetoceros compressus, Thalassiosira pseudonana, and Glenodinium foliaceum) gave a p H drift not inhibited by DIDS, but cultures of Chrysochromulina kappa, Gephrocapsa oceanica, and Coccolithus pelagicus, in which DLDS inhibited DIC uptake, did not gzve a pH dn$. This result shows that direct H C G transport may occur ! y a n anion exchange-type mechanism in some species but not others. Of the eighteen species investigated, only Heterosigma akashiwo did not have the potential fm direct uptake or extracellular U-catalyzed H C G utilization.Marine phytoplankton species acquire their inorganic carbon (Ci) for photosynthesis from the dissolved inorganic carbon (DIC) of the seawater.Within the usual seawater pH range of 8.0-8.3, the bulk of total DIC is HCOi, and CO, is less than 1 % of the total DIC (Skirrow 1975) when the system is in equilibrium with atmospheric CO,. Marine phytoplankton able to use HCO; may have a competitive advantage over phytoplankton using exclusively CO, when other essential nutrients or light are not rate-limiting for growth. The mechanism of DIC utilization is species dependent and some species can rapidly acclimate to changes in the concentration of dissolved CO, or total DIC (Coleman 1991, . In the direct uptake of HCO;

Extra and intracelular activities of carbonic anhydrase of the marine microalga Tetraselmis gracilis (Chlorophyta)

“…1b), whereas extracellular activity increased as a means of uptaking the bicarbonate ion, which became the major source of inorganic carbon as a result of alkalization. Similar profiles of extracellular CA activity along ten days of laboratory cultivation were observed for the microalgae Micromonas pusilla and Prorocentrum minimum (15,23,24).…”

“…The major species of dissolved inorganic carbon at the pH of seawater is the bicarbonate ion, which must be converted by the enzyme carbonic anhydrase (CA) to CO2, the substrate for the enzyme RUBISCO in photosynthesis (2,8,23). CA is a metalloenzyme, found in many organisms, and contains one atom of zinc essential for activity in its active site (34).…”

Competition of bloom-forming marine phytoplankton at low nutrient concentrations

“…Furthermore, elevated atmospheric CO 2 due to the increased industrial combustion of fossil fuels has decreased the pH values of seawater, hence decreasing the inorganic carbon utilization ability of S. costatum (Rost et al, 2003). However, the strategy of dinoflagellates to accommodate changing CO 2 concentrations is different from diatoms (Nimer et al, 1997). In natural environments, diatoms might be poor competitors due to the decreased phosphorus and silicate, together with the increasing atmospheric CO 2 .…”

Effects of pH on coastal marine phytoplankton

“…Further, there is no reason to expect all species to have the same physiological mechanism for their exhibited pH effects. For example, different species have different capabilities for production of extracellular carbonic anhydrase to speed up the equilibrium between bicarbonate and free CO 2 (Nimer et al 1997), a strategy to allow growth where free CO 2 may be limiting by metabolic drawdown of free CO 2 concentrations near the cell.…”