Tuesday, April 30, 2013
Exhibit Hall
The EPA has recommended a volume increase for biomass-based diesel production to 1 billion gallons for the year 2012. With increasing biodiesel production, the market is being flooded with crude glycerol, a by-product. Our aim is to convert crude glycerol to succinate by A. succinogenes 130Z. Succinate has been listed #1 on the DOE’s list of “Top Value Added Chemicals from Biomass”. A. succinogenes 130Z naturally produces high titers of succinate. It does not ferment glycerol but can metabolize glycerol via respiration in the presence of added terminal electron acceptors. Minimizing this respiratory metabolism is important for achieving a balance between biomass and succinate production. Batch cultures of A. succinogenes on glycerol under 1% O2‒99% CO2 gave high succinate yields, 67% and 76% for the wild-type strain and ΔpflB mutant, respectively. Similar experiments were performed in continuous cultures. Chemostat experiments were set up for steady state growth (D= 0.02 h-1) with constant dissolved O2 (gas mixture; 5% O2 + 95% CO2, gas flow rate; 2.5 ml min-1) in the fermentation medium. Succinate yields as high as 85% (wild-type strain) and 89% (ΔpflB mutant) were observed. These results suggest that optimizing the oxygen tension in the fermentation is a powerful way to increase succinate yields.