(724f) Using Metabolic Modeling to Examine Differences in the Metabolism of Chlorella Protothecoides Grown On Glucose Or Glycerol for the Production of Lipids for Biodiesel

Algae are a promising source of lipids for the production of biodiesel due to their high rates of lipid production, the ability for continuous culturing, and their use of non-arable land.  The microalga Chlorella protothecoides is known to grow to high cell densities with high lipid content when cultured on glucose.  We have previously shown that it maintains this high lipid content when grown on glycerol and exhibits an increased yield, albeit at the cost of slower productivity, showing glycerol to be a less expensive and higher yielding substrate.  In this work we have employed 13C-metabolic flux analysis (13C-MFA) to further examine the differences between its metabolism on glucose and its metabolism on glycerol during exponential growth.  The flux maps generated from 13C-MFA show a significantly higher flux rate through the oxidative pentose phosphate pathway during growth on glucose as well as a lower flux through the TCA cycle.  These results were compared to predictions generated by flux balance analysis, which had effectively demonstrated the increased yield of glycerol, but predicted it to have a lower flux through the TCA cycle than glucose, contrary to our 13C-MFA results.  We also conducted corollary maintenance studies using a CSTR system to determine the relative efficiencies of each substrate and the underlying factors influencing these differences.