COMPARATIVE STUDIES OF INORGANIC CARBON UTILIZATION IN EMILIANIA HUXLEYI AND SOME NON-CALCIFYING MARINE MICROALGAE

INTRODUCTIONMarinemicroalgaeacquiretheirinorganiccarbonforphotosynthesisfromseawaterwhereinorganiccarbonmaybepresentasfreeCO2 ,H2 CO3andHCO-3 andCO2 -3 .TheproportionsofdifferentDICformsareprimarilyrelatedtopH ,andtotemperatureandsalinitytoalessextent.ThetotalDICisashighas2mmol Linseawa terbutthisismainlyintheformofHCO-3 .InnormalpHrangeof7.8-8.2inseawater,HCO-3 accountsfororethan 90 %ofthetotalDIC,whilefreeCO2 islessthan1 % .TheequilibriumconcentrationoffreeCO2 isonly1 2 μm…

COMPARATIVE STUDIES OF INORGANIC CARBON UTILIZATION IN EMILIANIA HUXLEYI AND SOME NON-CALCIFYING MARINE MICROALGAE

Inorganic carbon utilization in the non calcifying marine microalgae, Nannochloropsis oculata, Phaeodactylum tricornutum and Porphyridium purpureum was compared with high and low calcifying strains of Emiliania huxleyi grown in artificial seawater medium aerated with either air (0.03% V/V CO 2) or CO 2 free air. For high calcifying strain of E. oculata and P. tricornutem , similar growth patterns were observed in air and CO 2 free air grown cultures. P. purpureum showed a less final cell density in CO 2 free air than in air grown culture. However, low calcifying strain of E. huxleyi was able to grow only in air grown culture, but not in CO 2 free air grown culture. Measurements of alkalinity, pH, concentration of dissolved inorganic carbon (DIC) and free CO 2 showed different patterns of DIC utilization. With N. oculata, P. tricornutum and P. purpureum the pattern of DIC utilization was characterized by an increase of pH and a decrease of DIC but a constant alkalinity in the cultures aerated with air or CO 2 free air, suggesting that bicarbonate utilization was concomitant with an efflux of OH -. Both alkalinity and pH were maintained rather constant in air grown culture of low calcifying strain of E. huxleyi, suggesting that diffusive entry of CO 2 could meet the requirement of DIC for its photosynthesis and growth. High calcifying strain of E.huxleyi , however, showed a pattern of decrease of alkalinity and DIC but an almost constant pH , indicating that bicarbonate was the major form of inorganic carbon utilised by this organism and bicarbonate uptake is unlikely to be accompanied by an efflux of OH -. The final pH values reached by N. oculata, P. tricornutum and P. purpureum in a closed system were 10.75, 10.60 and 9.85 respectively, showing that bicarbonate utilisation is concomitant with an efflux of OH . While the final pH of 8.4 in high calcifying E. huxleyi suggests that bicarbonate utilization was not accompanied by an efflux of OH -.