Simultaneous Transport of CO(2) and HCO(3) by the Cyanobacterium Synechococcus UTEX 625.

A mass spectrometer was used to simultaneously follow the time course of photosynthetic O(2) evolution and CO(2) depletion of the medium by cells of the cyanobacterium Synechococcus leopoliensis UTEX 625. Analysis of the data indicated that both CO(2) and HCO(3) (-) were simultaneously and continuously transported by the cells as a source of substrate for photosynthesis. Initiation of HCO(3) (-) transport by Na(+) addition had no effect on ongoing CO(2) transport. This result is interpreted to indicate that the CO(2) and HCO(3) (-) transport systems are separate and distinctly different transport systems. Measurement of CO(2)-dependent photosynthesis indicated that CO(2) uptake involved active transport and that diffusion played only a minor role in CO(2) acquisition in cyanobacteria.