Microaerobic Conversion of Glycerol to Ethanol in Escherichia coli

Abstract

ABSTRACTGlycerol has become a desirable feedstock for the production of fuels and chemicals due to its availability and low price, but many barriers to commercialization remain. Previous investigators have made significant improvements in the yield of ethanol from glycerol. We have developed a fermentation process for the efficient microaerobic conversion of glycerol to ethanol byEscherichia colithat presents solutions to several other barriers to commercialization: rate, titer, specific productivity, use of inducers, use of antibiotics, and safety. To increase the rate, titer, and specific productivity to commercially relevant levels, we constructed a plasmid that overexpressed glycerol uptake genesdhaKLM,gldA, andglpK, as well as the ethanol pathway geneadhE. To eliminate the cost of inducers and antibiotics from the fermentation, we used theadhEandicdpromoters fromE. coliin our plasmid, and we implemented glycerol addiction to retain the plasmid. To address the safety issue of off-gas flammability, we optimized the fermentation process with reduced-oxygen sparge gas to ensure that the off-gas remained nonflammable. These advances represent significant progress toward the commercialization of anE. coli-based glycerol-to-ethanol process.