Alternative CO2 concentrating mechanisms in different green algal species related to phosphorus limitation and pH

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Micro-algae are responsible for nearly one-half of all CO2 sequestration on the planet and they are increasingly used for biomass production to fuel our power plants and fix their fume-CO2. Algal CO2 fixation is thus a vital process that is supported by a CO2-concentrating mechanism (CCM) in many species. In freshwater (and marine) ecosystems CO2 concentrations are low, circa 15 μM, which requires a CCM to enhance carboxylation rates of the CO2-fixing enzyme Rubisco. This active process is assumed to require high inorganic phosphorus (Pi) concentrations, as found in the neutrophile Chlorella emersonii that has a high affinity CO2 uptake system under Pi replete conditions, but cannot realise its full CCM capacity under Pi limiting conditions. Recently, I discovered a contrasting pattern for the acidophile Chlamydomonas acidophila which realises a high affinity CO2 uptake system under both Pi replete and Pi limiting conditions. This questions the notion that CO2 uptake in C. acidophila is an active process. In addition, I have identified another algae with a third CCM strategy. I therefore propose to study the C-acquisition in these three algal species in conjunction with Pi concentration and pH to obtain mechanistic insight into algal functional responses to different conditions of CO2 and Pi. My collaboration with the Joint Genome Institute (USA), the University of Nebraska (USA), and Monash University (Australia) enables a multi-disciplinary approach that includes ecology, physiology, molecular biology and genetics to elucidate mechanisms underlying carbon sequestration in green micro-algae.