Original Papers

Archives of Microbiology

, Volume 159, Issue 1, pp 21-29

Effect of dissolved inorganic carbon on the expression of carboxysomes, localization of Rubisco and the mode of inorganic carbon transport in cells of the cyanobacterium Synechococcus UTEX 625

  • R. Michael L. McKayAffiliated withDepartment of Biology, McGill University
  • , Sarah P. GibbsAffiliated withDepartment of Biology, McGill University
  • , George S. EspieAffiliated withDepartment of Botany, Erindale College, University of Toronto

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In the cyanobacterium Synechococcus UTEX 625, the extent of expression of carboxysomes appeared dependent on the level of inorganic carbon (CO2+HCO inf3 sup- ) in the growth medium. In cells grown under 5% CO2 and in those bubbled with air, carboxysomes were present in low numbers (<2 · longitudinal section-1) and were distributed in an apparently random manner throughout the centroplasm. In contrast, cells grown in standing culture and those bubbled with 30 μl CO2 · 1-1 possessed many carboxysomes (>8 · longitudinal section-1). Moreover, carboxysomes in these cells were usually positioned near the cell periphery, aligned along the interface between the centroplasm and the photosynthetic thylakoids. This arrangement of carboxysomes coincided with the full induction of the HCO inf3 sup- transport system that is involved in concentrating inorganic carbon within the cells for subsequent use in photosynthesis. Immunolocalization studies indicate that the Calvin cycle enzyme ribulose bisphosphate carboxylase was predominantly carboxysome-localized, regardless of the inorganic carbon concentration of the growth medium, while phosphoribulokinase was confined to the thylakoid region. It is postulated that the peripheral arrangement of carboxysomes may provide for more efficient photosynthetic utilization of the internal inorganic carbon pool in cells from cultures where carbon resources are limiting.

Key words

Cyanobacteria Synechococcus Carboxysomes Ribulose bisphosphate carboxylase Immunogold localization CO2/HCO inf3 sup- transport