Photosynthesis and inorganic carbon utilization in Pleurochrysis sp. (Haptophyta), a coccolithophorid alga

Abstract

We studied and compared properties of inorganic carbon fixation for 2 coccolithophorid strains that differ in their capacity to calcify; namely high calcifying (HC) Pleurochrysis sp. CCMP 299 and low calcifying (LC) Pleurochrysis elongata CCAP 961/3. Pleurochrysis species are unicellular algae that, in nature and in culture, produce intracellular CaC03 encrusted structures (coccoliths). Pleurochrysis, and other calcifying algae, are potential players in atmospheric CO2 cycling and the maintenance of global carbon balances. In Pleurochrysis sp, and P. elongata (hereafter Pleurochrysis), photosynthesis was affected by increasing O2 (from 1 to 21 % in air), with 18% inhibition for LC cells and 9 % for HC cells. The inhibition could be reversed by (1) decreasing the ambient 02, (2) reducing the ambient pH (which rose in the medium, particularly for LC cells) and (3) by increasing the ambient inorganic carbon concentration. Carbonic anhydrase activity was detected in Pleurochrysis; HC cells having approximately 4 times more activity than LC cells. Inhibition of carbonic anhydrase by 0.25 mM acetazolamide (a non-membrane-permeating inhibitor of the enzyme) averaged 30% in HC cells and only 10% in LC cells. Calcium uptake measured for HC cells was 2.5 to 3.0 times higher in the light and 4 times higher in the dark than calcium uptake measured for LC cells. Rates of photosynthetic 0, evolution were significantly higher for both strains at acidic pH (e.g. 5.0, containing about 90% COz) than at seawater pH (e.g. 8.0, having about 1 % CO,), while at a basic pH (e.g. 9.0, virtually no CO2 and about 50% HC03-) rates were still substantial for HC cells but extremely low for LC cells. These data indicate that HC cells in their natural environment are primarily HC03-users. By comparing seawater COz concentrations (i.e. 15 FM) with calculated KO,(CO2), the CO2 concentration required for a halfmaximal rate of photosynthetic O2 evolution, for Pleurochrysis (51 and 37 pM for HC and LC cells, respectively) it follows that CO2 must be concentrated intracellularly for effective photosynthesis in both strains. Thus, an adequate CO2 supply depends on HC03-utilization and concomitant calcification, particularly in HC cells.

Environmental controls on coccolithophore calcification

“…This would reduce photoinhibition of photosynthesis by PAR and ultraviolet radiation (UVR) as well as the damage by UVR. However, a similar lack of photoinhibition at high PAR is seen when comparing lightly and heavily calcified strains (Israel & Gonzalez 1996) or when the degree of calcification is experimentally reduced (Paasche 1964, Paasche & Klaveness 1970, Nanninga & Tyrrell 1996, Trimborn et al 2007). However, Nielsen (1995) found a higher light-saturated rate of photosynthesis at a given inorganic carbon concentration in highly calcified cells than in cells with little calcification.…”

Limits to productivity of the algaPleurochrysis carterae(Haptophyta) grown in outdoor raceway ponds

“…Coccolithophorid algae, however, appear to be extremely sensitive to high oxygen concentrations. For example, Israel and Gonzalez (1996) showed high inhibition of photosynthesis by O 2 in P. carterae, and Shiraiawa et al (2004) also observed four to six times higher O 2 -inhibition in coccolithophorid algae compared to green microalgae. Our study of P. carterae reported here found similar results.…”

Bicarbonate addition promotes coral growth

“…Until recently, the general view has been that, at concentrations greater than 2 mM, DIC in seawater is in ample supply compared with other essential solutes such as nitrate and phosphate and trace elements such as iron, zinc, and silicon. There is, however, a growing awareness (Raven 1993) that the supply of DIC limits photosynthesis in planktonic algae, seagrasses (Beer and Rehnberg 1997), coccolithophores (Merrett et al 1993;Israel and Gonzales 1996), and macroalgae (Johnston et al 1992). Several authors (Muscatine et al 1989b;Weis et al 1989;Dubinsky et al 1990;Lesser et al 1994) have speculated on DIC limitation in coral.…”