The bloom-forming cyanobacterium Microcystis aeruginosa (Kütz.) Kütz. 854 was cultured with 1.05 W·m-2 ultraviolet-B radiation (UVBR) for 3 h every day, and the CO2-concentrating mechanism (CCM) within this species as well as effects of UVBR on its operation were investigated. Microcystis aeruginosa 854 possessed at least three inorganic carbon transport systems and could utilize external HCO3- and CO2 for its photosynthesis. The maximum photosynthetic rate was approximately the same, but the apparent affinity for dissolved inorganic carbon ...