Photosynthesis and Inorganic Carbon Usage by the Marine Cyanobacterium, Synechococcus sp

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Abstract
The marine cyanobacterium, Synechococcus sp. Nägeli (strain RRIMP N1) changes its affinity for external inorganic carbon used in photosynthesis, depending on the concentration of CO2 provided during growth. The high affinity for CO2 + HCO3− of air-grown cells (K½ < 80 nanomoles [pH 8.2]) would seem to be the result of the presence of an inducible mechanism which concentrates inorganic carbon (and thus CO2) within the cells. Silicone-oil centrifugation experiments indicate that the inorganic carbon concentration inside suitably induced cells may be in excess of 1,000-fold greater than that in the surrounding medium, and that this accumulation is dependent upon light energy. The quantum requirements for O2 evolution appear to be some 2-fold greater for low CO2-grown cells, compared with high CO2-grown cells. This presumably is due to the diversion of greater amounts of light energy into inorganic carbon transport in these cells.