Characterisation of CO(2) and HCO(3) (-) uptake in the cyanobacterium Synechocystis sp. PCC6803

The availability of a complete genome database for the cyanobacterium Synechocystis sp. PCC6803 (glucose-tolerant strain) has raised expectations that this organism would become a reference strain for work aimed at understanding the CO(2)-concentrating mechanism (CCM) in cyanobacteria. However, the amount of physiological data available has been relatively limited. In this report we provide data on the relative contributions of net HCO(3) (-) uptake and CO(2) uptake under steady state photosynthetic conditions. Cells were compared after growth at high CO(2) (2% v/v in air) or limiting CO(2) conditions (20 ppm CO(2)). Synechocystis has a very high dependence on net HCO(3) (-) uptake at low to medium concentrations of inorganic carbon (Ci). At high Ci concentrations net CO(2) uptake became more important but did not contribute more than 40% to the rate of photosynthetic O(2) evolution. The data also confirm that high Ci cells of Synechocystis sp. PCC6803 possess a strong capacity for net HCO(3) (-) uptake under steady state photosynthetic conditions. Time course experiments show that induction of maximal Ci uptake capacity on a shift from high CO(2) to low CO(2) conditions was near completion by four hours. By contrast, relaxation of the induced state on return of cells to high CO(2), takes in excess of 230 h. Experiments were conducted to determine if Synechocystis sp. PCC6803 is able to exhibit a 'fast induction' response under severe Ci limitation and whether glucose was capable of causing a rapid inactivation in Ci uptake capacity. Clear evidence for either response was not found.