INORGANIC CARBON TRANSPORT IN RELATION TO CULTURE AGE AND INORGANIC CARBON CONCENTRATION IN A HIGH‐CALCIFYING STRAIN OF EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)¹

Abstract

The relationships among inorganic carbon transport, bicarbonate availability, intracellular pH, and culture age were investigated in high‐calcifying cultures of Emiliania huxleyi (Lohmann) Hay & Mohler. Measurement of inorganic carbon transport by the silicone‐oil centrifugation technique demonstrated that gadolinium, a potential Ca2+ channel inhibitor, blocked intracellular inorganic carbon uptake and photosynthetic 14CO2+ fixation in exponential‐phase cells. In stationary‐phase cells, the intracellular inorganic carbon concentration was unaffected by gadolinium. Gadolinium was also used to investigate the link between bicarbonate and Ca2+ transport in high‐calcifying cells of E. huxleyi. Bicarbonate availability had significant and rapid effects on pHi in exponential‐ but not in stationary‐phase cells. 4′, 4′‐Diisothiocyanostilbene‐2,2′‐disulfonic acid did not block bicarbonate uptake from the external medium by exponential‐phase cells. Inorganic carbon utilization by exponential‐ and stationary‐phase cells of Emiliania huxleyi was investigated using a pH drift technique in a closed system. Light‐dependent alkalization of the medium by stationary‐phase cells resulted in a final pH of 10.1 and was inhibited by dextran‐bound sulphonamide, an inhibitor of external carbonic anhydrase. Exponential‐phase cells did not generate a pH drift. Overall, the results suggest that for high‐calcifying cultures of E. huxleyi the predominant pathway of inorganic carbon utilization differs in exponential and stationary phase cells of the same culture.

Response of the coccolithophores Emiliania huxleyi and Coccolithus braarudii to changing seawater Mg2+ and Ca2+ concentrations: Mg/Ca, Sr/Ca ratios and δ44/40Ca, δ26/24Mg of coccolith calcite

“…huxleyi and C. braarudii achieved maximum rates of inorganic carbon production at seawater [Ca 2+ ] of %10 mmol L À1 , suggesting a well established and adjusted calcification mechanism to the calcium concentration of the modern ocean. Parallel to our findings Nimer et al (1996), Trimborn et al (2007), Herfort et al (2004) and Leonardos et al (2009) reported increasing trends for PIC prod in E. huxleyi from 1 to 10 mmol Ca L À1 . As observed previously by Herfort et al (2004), calcification rate of E. huxleyi was reduced at seawater [Ca 2+ ] >20 mmol L À1 , whereas calcification rate of C. braarudii remained constant with increasing [Ca 2+ ].…”

Carbon dioxide‐concentrating mechanism and the development of extracellular carbonic anhydrase in the marine picoeukaryote Micromonas pusilla

“…The development of activity of CA ext in M. pusilla under conditions of CO # -limitation is similar to that in the diatoms Skeletonema costatum (Nimer, Warren & Merrett, 1998), Thalassiosira rotula and Thalassiosira weisfloggi (Nimer et al, 1997) but differs from the coccolithophorid Emiliania huxleyi (Nimer, Merrett & Brownlee, 1996) and the diatom Phaeodactylum tricornutum (Iglesias-Rodrı! guez & Merrett, 1997) where exofacial CA ext activity is regulated by the concentrations of CO # and HCO $ − .…”

Effect of growth rate and CO2 concentration on carbon isotopic fractionation by the marine diatom Phaeodactylum tricornutum

“…However, simple calculations indicate that the supply of CO, should rarely be limiting to phytoplankton photosynthesis in the oceans, and the laboratory conditions under which bicarbonate uptake has been clearly demonstrated seem atypical of the natural marine environment. It is reasonable to conclude that with the exception of calcareous algae (Nimer et al 1996) virtually all synthesis of organic matter by marine phytoplankton is based on CO, uptake and the C, pathway rather than by active transport of bicarbonate.…”