Cyanobacterial Mutants Defective in HCO₃ ^- Uptake

Abstract

Photosynthetic microorganisms are capable of adapting to a wide range of CO₂ concentrations. When cyanobacterial cells are transferred from high to low concentrations of CO₂, they undergo an adaptation process. This includes modulation of the expression of certain genes, some of which are involved in the operation of the inorganic carbon (Ci)-concentrating mechanism (CCM, see Miller et al. 1990; Kaplan et al. 1991; Raven 1991; Badger, Price 1992; Ogawa 1993 and Kaplan et al. 1994 for recent reviews and literature citations). The active accumulation of Ci to levels as high as 50-100 mM Ci, consequent on the activity of the CCM, enables the cells to perform efficient photosynthesis in spite of the relatively low affinity of their ribulose 1,5- bisphosphate carboxylase (rubisco) for CO₂. Moreover, the elevated concentration of CO₂ in close proximity to rubisco, within the carboxysomes, activates the enzyme, reduces competition by O₂ and inhibits photorespiration (Schwarz et al. 1995)