(629a) Engineering Escherichia coli for Utilization of Ethylene Glycol

Ethylene glycol (EG) is an important chemical that has a wide range of industrial applications, including the manufacturing of polyester plastics such as polyethylene terephthalate (PET). Over 25 million tons of PET are synthesized annually to produce plastic bottles, with EG as a raw material. Due to an increase in global consumption and its persistent negative effect on environmental pollution, the accumulation of PET plastics is a growing concern. If PET wastes can be cost-effectively hydrolyzed, the resulting hydrolyzed PET monomers may be a source of cheap and abundant feedstock to produce useful chemicals.

EG can be a major product when cellulosic biomass is chemically hydrolyzed and hydrogenated. It has the largest market and is expected to reach USD 33.26 billion by 2020. However, the purification of EG from the mixture of other polyols that are generated by the chemical process is not cost-effective. Thus, converting this EG from the cellulose waste and PET waste into microbial biomass or products could contribute to developing a solution for the worldwide concern over the related environmental issues.

The utilization of non-conventional substrates such as EG has not been explored widely in Escherichia coli. The wildtype E. coli is unable to metabolize EG, although it has the potential genes for this purpose. It can be metabolized aerobically through C2 metabolic pathways via the intermediates glycolaldehyde and glycolate. In this study, we have engineered E. coli to enable EG utilization via simultaneous overexpression of L-1,2-propanediol oxidoreductase (encoded by fucO gene) and aldehyde dehydrogenase A (encoded by aldA gene). Overexpression of fucO and aldA with a constitutive promoter (PgyrA), improved the cell growth on EG as the major carbon source. EG utilization was further improved with the supplementation of a low concentration of glycerol or amino acids. The engineered strain completely consumed up to 20 g/L of ethylene glycol in 72 hours without any process optimization. Overall, this study provides an E. coli strain that can utilize EG efficiently. With future improvements, this strain can potentially produce valuable chemicals from raw EG that are derived from plastic and cellulose wastes.