CO₂ CONCENTRATING MECHANISMS IN ALGAE: Mechanisms, Environmental Modulation, and Evolution

Abstract

The evolution of organisms capable of oxygenic photosynthesis paralleled a long-term reduction in atmospheric CO2 and the increase in O2. Consequently, the competition between O2 and CO2 for the active sites of RUBISCO became more and more restrictive to the rate of photosynthesis. In coping with this situation, many algae and some higher plants acquired mechanisms that use energy to increase the CO2 concentrations (CO2 concentrating mechanisms, CCMs) in the proximity of RUBISCO. A number of CCM variants are now found among the different groups of algae. Modulating the CCMs may be crucial in the energetic and nutritional budgets of a cell, and a multitude of environmental factors can exert regulatory effects on the expression of the CCM components. We discuss the diversity of CCMs, their evolutionary origins, and the role of the environment in CCM modulation.

How will Ocean Acidification Affect Baltic Sea Ecosystems? An Assessment of Plausible Impacts on Key Functional Groups

“…Most macroalgae have CO 2 concentrating mechanisms (CCMs), which reduce their dependency on ambient CO 2 (or HCO 3 -) concentrations. Therefore, these taxa have been assumed to be largely insensitive to acidification (Giordano et al 2005). There are no published results for the effects of ocean acidification on Baltic Sea macroalgae, but recent work elsewhere confirms that species with CCMs are likely to be unaffected by, or may benefit marginally from, ocean acidification (Hepburn et al 2011).…”

“…Here again, relatively little work has been done on Baltic Sea species or populations. The prevalence of CCMs in phytoplankton has been suggested as a reason to expect reduced sensitivity to ocean acidification (Giordano et al 2005;Hopkinson et al 2011). For spring bloom species, recent results for the diatom Skeletonema marinoi from the Skagerrak showed that the effects of ocean acidification on growth rate differed between strains and populations but overall, growth of S. marinoi was not affected by increased pCO 2 (750 latm; Kremp et al unpublished results).…”

Interactions between CCM and N2 fixation in Trichodesmium

“…All cyanobacterial species investigated to date, however, possess mechanisms to enhance the carboxylation efficiency of their RubisCO, reducing the risk of carbon limitation. These processes are commonly referred to as CO 2 concentrating mechanisms (CCMs; Badger et al 2006;Giordano et al 2005;Kaplan and Reinhold 1999). Although CCM functioning should significantly repress the oxygenase function of RubisCO (Colman 1989), photorespiration has recently been found to occur under certain conditions in Synechocystis PCC6803 (Eisenhut et al 2008).…”

Sensing inorganic carbon: CO2 and HCO3−

“…CO 2 is the product of all decarboxylase reactions examined so far, including those which operate in vivo close to equilibrium and which can also function as carboxylases. Those carboxylases which are essentially irreversible in vivo can, depending on the enzyme involved, use either CO 2 or HCO 3 − [1]. These carboxylation and decarboxylation reactions are major links in the biogeochemical cycle of carbon, each accounting for a global flux of at least 10 Pmol (10 15 mol) of carbon each year [1].…”

“…These carboxylation and decarboxylation reactions are major links in the biogeochemical cycle of carbon, each accounting for a global flux of at least 10 Pmol (10 15 mol) of carbon each year [1]. A group of enzyme which can react with both CO 2 and HCO 3 − are the polyphyletic carbonic anhydrases (EC 4.2.1.1) which catalyse the interconversion of CO 2 and HCO 3 − ; the uncatalysed reaction is frequently slow relative to metabolic fluxes of the inorganic carbon species [1].…”