Massive Inorganic Carbon Cycling in Cyanobacteria Geared to the Energy Transfer to PSII
Light energy-dependent mechanisms which raises the concentration of CO2 at the carboxylating sites (CCM) have been recognized in many photosynthetic microorganisms . We have followed CO2 and HCO3- fluxes associated with the CCM in several photosynthetic organisms. Sustained net CO2 efflux was observed during net photosynthesis in certain marine organisms including the cyanobacterium Synechococcus sp. WH7803  and Nannochloropsis sp. . This efflux resulted from HCO3- uptake and interacellular conversion to CO2, part of which leaked and raised its concentration in the cell vicinity. On the other hand, the steady state [CO2] near photosynthesizing microorganisms, including the fresh water Synechococcus sp. PCC 7942, is often lower than expected at CO2/HCO3- chemical equilibrium , a phenomena attributed to CO2 uptake and fixation during photosynthesis.
Key wordsCO2-concentrating mechanism Cyanobacteria
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