Effect of Cl − on photosynthetic bicarbonate uptake in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803

Photosynthetic inorganic carbon utilization was investigated in two cyanobacteria Microcystis aeruginosa and Synechocystis PCC6803 grown in standing culture. Photosynthetic rates for the two algae reached about 10 times the theoretical CO2 supply rate at low dissolved inorganic carbon (DIC) of 100 μmol/L, and the rates were unaffected by the addition of 20 mmol/L Na+, indicating that the two algae possessed Na+-independent HCO 3 − utilization for photosynthesis under low DIC. Their photosynthetic rates at low DIC were inhibited by higher Cl− and the degrees of inhibition were increased with the rise of Cl− concentration, and in the presence of Diphenylamine-2-carboxylate (DPC), a reported Cl− channel inhibitor, the rates decreased by 74%–82%, implying that putative DPC-sensitive Cl− channels participate in Na+-independent HCO 3 − uptake for photosynthesis. The experiment of intracellular 14C-DIC accumulation for photosynthesis showed that internal DIC pools decreased by about 80% with 200 μmol/L DPC and by 64%–70% with 100 mmol/L Cl−. The experiment of chlorophyll a fluorescence quenching showed that initial rates and extents of fluorescence quenching obviously decreased with 200 μmol/L DPC or 100 mmol/L Cl−. The two experiments gave further evidence that putative DPC-sensitive Cl− channels participate in Na+-independent HCO 3 − uptake for photosynthesis in the two algae grown in standing culture.