(472g) Nutrient Deficiency Leads to Overflow Metabolism in Glucose-Fed Chromochloris Zofingiensis

Chromochloris zofingiensis is an emerging model system for the production of biofuels and bioproducts that is attractive due to its lipid and astaxanthin production capability. Astaxanthin is a high value product with uses in the pharmaceutical, nutraceutical, and cosmetic industries. This organism demonstrates high levels of triacylglycerol accumulation when additional organic carbon sources are provided, making it ideal for metabolic or genetic engineering focused on increasing algal lipid production. A genome scale metabolic model, iCzof1915, was constructed for this organism, and used to conduct flux balance analysis (FBA) studies for different media conditions. The results of FBA simulations conducted using this model predicted the excretion of lactate when C. zofingiensis is grown on glucose, which was later confirmed with spent media metabolomics data. To investigate whether this behavior was due to low oxygen availability in the cultures, an experiment was conducted in a steady-state continuously operating bioreactor. Conditions within the reactor remained aerophilic, and lactate secretion was still observed. During growth on glucose in nutrient dense media, the production of fermentation products is not observed. A ¹³C-MFA study was done to compare metabolic function in C. zofingiensis cultures in different media and light conditions. Cultures in the nutrient dense media type with higher iron and magnesium content resulted in higher TCA cycle fluxes and allowed for carbon fixation, while in the low iron media formulation 44% of carbon uptake from glucose is directed to fermentation products and photosynthetic activity is shut down even in continuous illumination. ATP yield on glucose and biomass productivities were substantially higher for growth in the nutrient dense media type. The results of these experiments show that nutrient deficiency in C. zofingiensis leads to overflow metabolism and sub-optimal metabolic function.