Synechocystis sp. PCC6803 actively uptake inorganic carbon to elevate the carbon dioxide concentration around their Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) enzyme. The mechanism is comprised of a set of enzymatic complexes which act in an orchestrated manner to transfer extracellular dissolved inorganic carbon into the cell and concentrate it within a specialized compartment. NADPH dehydrogenase-1 is the first operational super-complex in light conditions and, therefore, allows a direct estimation of carbon flux into the cell, albeit before photosynthesis and the concentrating mechanism reach a chemical steady-state condition. We calculated the uptake rate during this period by fitting a nonlinear function to the sharp decline in the CO2 gas exchange profile recorded with membrane inlet mass spectrometry, considering the constant change in rate during this step. We estimate the carbon dioxide uptake rates and pool sizes, showing that these values correspond to previously reported steady state rates in the literature. During the investigation, we reveal new properties of the uptake mechanism. At pH lower than six, the enzymatic complex responsible for the CO2 uptake becomes inactive. Its activity recovers within minutes when attenuating the pH within the cell or elevating it back at or above pH 6.0 outside the cell, a characteristic which seems to be conserved in activity in Symbiodinium microadriaticum, Isochrysis galbana, Phaeodactylum tricornutum and Emiliania huxleyi. We, therefore, suggest that within the carbon concentrating mechanism, CO2 insertion processes can be deactivated when the organism faces pH 5.7.
Bibliographical noteFunding Information:
We would like to thank Prof. Michael Gurevich from the George S. Wise Faculty for Life Sciences at Tel-Aviv University for his advice regarding writing and editing this manuscript, and Prof. Nir Keren from the Department of Plant and Environmental Science at the Hebrew University of Jerusalem for his contribution of the organism strains. The authors would like to extend their gratitude to Photon Systems Instruments Ltd. for their collaboration on this project. This research was supported by EU FP7 Marie Curie Initial Training Network HARVEST (FP7 Project No. 238017 ).
© 2018 The Authors
- Gas exchange
- Synechocystis sp. PCC6803
ASJC Scopus subject areas
- Agronomy and Crop Science