Utilization of inorganic carbon by marine microalgae

Bruce D. Burns, John Beardall

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Six species of marine microalgae, namely Phaeodactylum tricornutum Bohlin, Dunaliella tertiolecta Butcher, Isochrysis galbana Parke, Porphyridium purpureum (Bory) Ross, Chroomonas sp., and Oscillatoria woronichinii Aniss., have been examined with respect to their gas exchange characteristics and the inorganic carbon species taken up by the cells from the bulk medium. All species showed a high affinity, in photosynthesis, for inorganic carbon with K 1 2(Dic), in the range 7.6-39.8 μM [K 1 2(Co2) 0.25-1.35 μM] and low CO2 compensation concentrations (≤0.3μM). Such data are suggestive of operation of a "CO2-concentrating mechanism" in these microalgae. Direct measurements of internal inorganic carbon pools in four of the species studied confirm this (O. woronichinii and Chroomonas were not tested). By comparison of achieved photosynthetic rates with calculated rates of CO2 supply from the dehydration of bicarbonate, it was shown that Phaeodactylum, Porphyridium, and Dunaliella could utilize the bicarbonate present in the medium. Data for the other species were inconclusive although the pH dependence of K 1 2(Co2) for photosynthesis by Oscillatoria indicated that this species too could utilize bicarbonate. Such observations could, however, not be used as evidence that, at least in the eucaryotic algae examined, bicarbonate was the inorganic carbon species crossing the plasmalemma as Phaeodactylum, Porphyridium, Dunaliella, and Isochrysis all showed the presence of carbonic anhydrase activity in intact cells as well as in crude extracts. "External" carbonic anhydrase activity represented from 1 4to 1 2 of the total activity in the cells of these algae. It is concluded that, as a consequence of a CO2-concentrating mechanism, photorespiration was suppressed in the marine microalgae examined although the data obtained did not allow any firm conclusions to be drawn regarding the species of inorganic carbon transported into the cell.

Original languageEnglish
Pages (from-to)75-86
Number of pages12
JournalJournal of Experimental Marine Biology and Ecology
Issue number1
Publication statusPublished - 13 Apr 1987


  • Bicarbonate
  • CO accumulation
  • Microalga
  • Photosynthesis

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