Chapter 8 - The CO2-Concentrating Mechanism and Carbon Assimilation

Abstract

This chapter discusses CO2 concentrating mechanisms.Photosynthetic carbon metabolism, photorespiratory metabolism, and acetate metabolism are described to emphasize the metabolism of carbon assimilation. CCMs represent an evolutionary adaptation acquired by microalgae and cyanobacteria in response to increased O2 and decreased CO2 availability, especially in aquatic environments. Photosynthetic organisms absorb CO2 as the major substrate to support photosynthesis, the beginning of energy flow into living organisms and one of the primary processes comprising the global carbon cycle. Therefore, changes in CO2 concentrations can have a profound impact on photosynthesis and many related processes in carbon metabolism, which subsequently influence the biotic environment of earth. In addition to a variable supply from respiratory sources, equilibration of CO2 between aqueous environments and the atmosphere is relatively slow, which can result in a depletion of the aqueous CO2 during active photosynthesis. Adding a further challenge, the roughly 104-fold slower diffusion of CO2 in water versus air greatly exacerbates the problem of CO2 supply to Rubisco.