Calcification and utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi Lohmann

Abstract

SUMMARYThe relationship between inorganic-carbon dependent photosynthetic oxygen eyolution and calcification was investigated m high-and low-calcifying strains of Emiliania huxleyi showing a ten-fold difference in calcification rate. Unlike the low-calcifying strain calcifying cultures showed a four-fold increase in inorganic carbon (1 mM) dependent photosynthetic oxygen over the pH range 5-8-3 resulting in a 20 fold difference in photosynthetic rate between the two strains at pH 8-3. Calcifying cells have a high affinity for HCO^ , the concentration of dissolved inorganic carbon [DIC] required for half-maximal rate of photosynthetic O, evolution {K^..^ [DIC]) being 200/<M at pH 8-3. In mid-exponential phase cultures the stoichiometry between "CO, fixation and calcification was 1 :1 so it IS likely that the high photosynthetic rate at pH 83 is sustained by '^c6., released from H "CO^ during calcification.Measurement of bicarbonate transport by the silicone-oil-layer centrifugal filtering technique demonstrated a rapid uptake and achievement of equilibrium (less than 3 s) between the lntracellular and external inorganic carbon concentrations in low and high-calcifying cells. Subsequent metabolism of the "C intracellular inorganic carbon pool did not occur in low-calcifying cells suggesting the block m calcification occurs either in transport into or within the coccolith vesicle.

The mitigating effect of calcification-dependent of utilization of inorganic carbon of Chara vulgaris Linn on NH4-N toxicity

“…3 and 4 Tables 1 and 2) conformed to the hypothesis 2. Similar result was also reported in coccolithophorid as that extant HCO À 3 significantly increased calcification rate of Emiliania huxleyi Lohmann (Nimer and Merrett, 1992).…”

Calcification rate and temperature effects on Sr partitioning in coccoliths of multiple species of coccolithophorids in culture

“…However, ''instantaneous'' calcification rate determinations (via 14 C incorporation) and determinations of integrated calcite production in previous culture experiments with E. huxleyi are consistent and suggest rather continuous calcite production during the photoperiod (e.g. Nimer and Merrett, 1992;Dong et al, 1993).…”

Dissolved inorganic carbon utilization and the development of extracellular carbonic anhydrase by the marine diatom Phaeodactylum tricornutum

“…Under conditions when CO,^ is rate-limiting for photosynthesis, marine phytoplankton species able to use HCO3~ might have a competitive advantage over those species unable to use HCO3", Two mechanisms of HCO3" utilization have been demonstrated in niarine phytoplankton. Some species employ direct HCO,," utilization, which depends on the transport of the bicarbonate ion across the plasma membrane into the cytosol (Colman & Gehl, 1983;Rees, 1984;Dixon et al, 1987;Nimer & Merrett, 1992;Colman & Rotatore, 1995;Merrett, Nimer & Dong, 1996), The other mechanism is the indirect utilization of HCO3 , in which CO,^ is produced by the dehydration of HCO3^ in the unstirred layer outside the plasma membrane, a process facilitated by extracellular CA (Tsuzuki, 1983;Tsuzuki & Miyachi, 1989), The inhibition of extracellular CA by DBS (Haglund et al, 1992;Nimer, Merrett & Brownlee, 1996) demonstrates the importance of this enzyme in the production of COj in the unstirred layer (Fig, 3), The proportion of photosynthetic '^CO,, fixation inhibited by DBS shows the contribution made by the catalytic production of CO.j in the unstirred layer to the total flux of CO,, into the cell and subsequent photosynthetic fixation.…”

“…strain 10-52/6) were grown on modified f/2 (Paasche, 1964;Nimer & Merrett, 1992) at the same pH, with NO.," and total DIC concentrations as in f/2 (Guillard & Ryther, 1962) and ASP-2 media (Provasoli, McLaughlin & Droop, 1957). All media were filter-sterilized and, when required, buffered at pH 8-3 with 25 mM Tricine (A^-tris-[Hydroxymethyl] methylglycine; Af-[2-Hydroxy-l ,l-bis(hydroxymethyl)ethyl]glycine).…”