Abstract

The marine diatom, Phaeodactylum tricornutum Bohlin, is probably one of the most extensively studied marine alga with respect to carbon acquisition and assimilation mechanisms. However, quantitative analyses of HCO₃^-utilization and the detailed process of acclimation of cells from high CO₂ to limited CO₂ are yet to be done extensively. Suitable molecular markers for this acclimation process are not established, either. Recently, it became clear that the rate of CO₂ formation in artificial seawater is about eight times slower than that in freshwater, and thatP. tricornutum cells utilize HCO₃^- quite efficiently. Despite their great capacity to take up HCO₃^-, the signal controlling photosynthetic affinity for dissolved inorganic carbon has been shown to be CO₂ in the medium. Furthermore, light seems to be required for this process.

Internal carbonic anhydrase (CA) activity has been shown to be crucial for high-affinity photosynthesis in a number of algae, including marine diatoms. Internal β-type CA, which has been isolated in one strain of P. tricornutum, was clearly shown to be a low-CO₂ inducible enzyme. This review paper additionally includes data showing that this CA occurs generally in P. tricornutum species.