Growth and Photosynthesis of the Cyanobacterium Synechococcus leopoliensis in HCO3−-Limited Chemostats

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Abstract
S. leopoliensis was grown in HCO3--limited chemostats. Growth at 50% the maximum rate occurred when the inorganic C concentration was 10-15 .mu.M (or 5.6 to 8.4 nM CO2). The O2 to CO2 ratios during growth were as high as 192,000 to 1. At growth rates < 80% the maximum rate, essentially all the supplied inorganic C was converted to organic C, and the cells were C limited. C-limited cells used HCO3- rather than CO2 for growth. They also exhibited a very high photosynthetic affinity for inorganic C in short-term experiments. Cells growing at > 80% maximum growth rate, in the presence of high dissolved inorganic C, were termed C sufficient. These cells had photosynthetic affinities that were .apprx. 1000-fold lower than HCO3--limited cells and also had a reduced capacity for HCO3- transport. HCO3--limited cells are reminiscent of the air-grown cells of batch culture studies while the C sufficient cells are reminiscent of high-CO2 grown cells. The low affinity cells of the present study were growing at CO2 concentrations less than air saturation. Supranormal levels of CO2 are apparently not required to induce the physiological changes usually ascribed to high CO2 cells.