Production of succinate from simply purified crude glycerol by engineered Escherichia coli using two-stage fermentation

Background: Crude glycerol is a main by-product from biodiesel production, and efficient utilization of crude glycerol will bring significant economic and environmental benefits. However, the complex compositions of crude glycerol may impair the cellular growth and inhibit the crude glycerol consumption. Therefore, it is necessary to find a simple method to treat the crude glycerol and release the inhibition on cell metabolism. Results: The simply purified crude glycerol by activated carbon can be used as the carbon source to produce succinate in two-stage fermentation by the engineered Escherichia coli strain, MLB(IdhA(-),pflB(-)) expressing phosphoenolpyruvate carboxykinase. In the flask experiments, succinate production from crude glycerol without treatment was less than that from pure glycerol. However, in the experiments of 1.5-L bioreactor, little succinate was produced in crude glycerol. The simply purified crude glycerol was used as carbon source for succinate production, and the glycerol consumption and succinate production were enhanced greatly. The succinate produced from the simply purified crude glycerol reached 566.0 mM, which was about ten times higher as that of non-purified one (50.3 mM). The succinate yield of the anaerobic stage achieved 0.97 mol/mol, which was 97% of the theoretical yield. Conclusion: The treatment of crude glycerol by activated carbon could effectively release the inhibition on the glycerol consumption and succinate production of the engineered E. coli strains, so that the fermentation result of the treated crude glycerol was similar as the pure glycerol. The results showed that the metabolically engineered E. coli strains have great potential to produce succinate from crude glycerol.