One of the most pressing grand challenges for the 21st century is to sustainably support the growing human population, predicted to increase to 9 billion people by mid-century. Meeting this challenge will require the development of new and innovative renewable production systems. One approach is to capture carbon dioxide (CO2) and convert this greenhouse gas into useful products. Algae represent an exciting potential renewable source of products due to their ability to convert CO2 together with light into valuable bioproducts including antioxidants and biofuels. In this work, we have studied in detail the metabolic fluxes of carbon fixation in the micro-algae Chlorella vulgaris UTEX 395 under three different growth conditions: photoautotrophic (CO2 + light), mixotrophic (CO2 + glucose + light) and heterotrophic growth (glucose, no light), at three different CO2 levels: ambient air (~0.04% CO2), air + 1% CO2, and air + 5% CO2. Metabolic fluxes were quantified using 13C-labeling experiments, followed by mass spectrometry (GC-MS) analysis of 13C-labeling and 13C-metabolic flux analysis. In these experiments, we also measured net production and consumption of CO2 and O2 in real time using an on-line process mass spectrometer to further improve flux resolution. This allowed us, for the first time, to quantitatively map metabolic fluxes of micro-algae under a wide range of growth conditions. Through this work we have identified new targets for improving carbon fixation efficiency under different growth regimes. Second, we studied dynamic metabolic changes of C. vulgaris during light-dark cycles (14 hr light, 10 hr dark), specifically under photoautotrophic and mixotrophic growth conditions with ambient air (~0.04% CO2), air + 1% CO2, and air + 5% CO2. Through dynamic metabolic flux measurements we identified inefficiencies in carbon metabolism at late stage of the dark cycle. This also provides opportunities to further enhance carbon fixation efficiency of this organism. In summary, through this work we have established new insights into the metabolism of the micro-algae Chlorella vulgaris and have new identified metabolic engineering targets to improve carbon fixation efficiency.

Metabolic flux analysis of the micro-algae Chlorella vulgaris at different CO2 concentrations under autotrophic, heterotrophic, and mixotrophic growth

249th National Meeting (2015)

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