Evidence for HCO3− Transport by the Blue-Green Alga (Cyanobacterium) Coccochloris peniocystis

Abstract

The possibility of HCO₃⁻ transport in the blue-green alga (cyanobacterium) Coccochloris peniocystis has been investigated. Coccochloris photosynthesized most rapidly in the pH range 8 to 10, where most of the inorganic C exists as HCO₃⁻. If photosynthesis used only CO₂ from the external solution the rate of photosynthesis would be limited by the rate of HCO₃⁻ dehydration to CO₂. Observed rates of photosynthesis at alkaline pH were as much as 48-fold higher than could be supported by spontaneous dehydration of HCO₃⁻ in the external solution. Assays for extracellular carbonic anhydrase were negative. The evidence strongly suggests that HCO₃⁻ was a direct C source for photosynthesis.