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 (ldhA − , 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.
Hydroxy fatty acids (HFAs) are valuable compounds that are widely used in medical, cosmetic and food fields. Production of ω-HFAs via bioconversion by engineered Escherichia coli has received a lot of attention because this process is environmentally friendly. In this study, a whole-cell bio-catalysis strategy was established to synthesize medium-chain ω-HFAs based on the AlkBGT hydroxylation system from Pseudomonas putida GPo1. The effects of blocking the β-oxidation of fatty acids (FAs) and enhancing the transportation of FAs on ω-HFAs bio-production were also investigated. When fadE and fadD were deleted, the consumption of decanoic acid decreased, and the yield of ω-hydroxydecanoic acid was enhanced remarkably. Additionally, the co-expression of the FA transporter protein, FadL, played an important role in increasing the conversion rate of ω-hydroxydecanoic acid. As a result, the concentration and yield of ω-hydroxydecanoic acid in NH03(pBGT-fadL) increased to 309 mg/L and 0.86 mol/mol, respectively. This whole-cell bio-catalysis system was further applied to the biosynthesis of ω-hydroxyoctanoic acid and ω-hydroxydodecanoic acid using octanoic acid and dodecanoic acid as substrates, respectively. The concentrations of ω-hydroxyoctanoic acid and ω-hydroxydodecanoic acid reached 275.48 and 249.03 mg/L, with yields of 0.63 and 0.56 mol/mol, respectively. This study demonstrated that the overexpression of AlkBGT coupled with native FadL is an efficient strategy to synthesize medium-chain ω-HFAs from medium-chain FAs in fadE and fadD mutant E. coli strains.
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