Metabolic engineering of Escherichia coli for the de novo stereospecific biosynthesis of 1,2-propanediol through lactic acid

1,2-propanediol (1,2-PDO) is an industrial chemical with a broad range of applications, such as the production of alkyd and unsaturated polyester resins. It is currently produced as a racemic mixture from nonrenewable petroleum-based feedstocks. We have reported a novel artificial pathway for the biosynthesis of 1,2-PDO via lactic acid isomers as the intermediates. The pathway circumvents the cytotoxicity issue caused by methylglyoxal intermediate in the naturally existing pathway. Successful <i>E. coli</i> bioconversion of lactic acid to 1,2-PDO was shown in previous report. Here, we demonstrated the engineering of <i>E. coli</i> host strains for the <i>de novo</i> biosynthesis of 1,2-PDO through this pathway. Under fermenter-controlled conditions, the <i>R</i>-1,2-PDO was produced at 17.3 g/L with a molar yield of 42.2% from glucose, while the <i>S</i>-isomer was produced at 9.3 g/L with a molar yield of 23.2%. The optical purities of the two isomers were 97.5% <i>ee</i> (<i>R</i>) and 99.3% <i>ee</i> (<i>S</i>), respectively. To the best of our knowledge, these are the highest titers of 1,2-PDO biosynthesized by either natural producer or engineered microbial strains that are published in peer-reviewed journals.