Chemo-biological upcycling of poly(ethylene terephthalate) (PET) developed in this study includes the following key steps: chemo-enzymatic PET depolymerization, biotransformation of terephthalic acid (TPA) into catechol, and its application as a coating agent. Monomeric units were first produced through PET glycolysis into bis(2-hydroxyethyl) terephthalate (BHET), mono(2-hydroxyethyl) terephthalate (MHET), and PET oligomers, and enzymatic hydrolysis of these glycolyzed products using Bacillus subtilis esterase (Bs2Est). Bs2Est efficiently hydro-lyzed glycolyzed products into TPA as a key enzyme for chemoenzymatic depolymerization. Furthermore, catechol solution produced from TPA via a whole-cell biotransformation (Escherichia coli) could be directly used for functional coating on various substrates after simple cell removal from the culture medium without further purification and water-evaporation. This work demonstrates a proof-of-concept of a PET upcycling strategy via a combination of chemo-biological conversion of PET waste into multifunctional coating materials.

We report metabolic engineering of Corynebacterium glutamicum (C. glutamicum) for high-level production of 5-hydroxyvaleric acid (5-HV), an important C5 platform chemical covering a wide range of industrial applications, using glucose as a sole carbon source. To derive 5-HV, an artificial 5-HV biosynthesis pathway, composed of the first three reaction steps of an l-lysine catabolic pathway via 5-aminovaleramide along with a subsequent intracellular reduction step, was constructed: l-lysine was converted to glutarate semialdehyde through an l-lysine catabolic pathway encoded by Pseudomonas putida davTBA genes, and glutarate semialdehyde was further reduced to 5-HV by a suitable aldehyde reductase. Various aldehyde reductases including CpnD from Clostridium aminovalericum, Gbd from Ralstonia eutropha, ButA from C. glutamicum, and YihU, YahK, and YqhD from Escherichia coli were examined for efficient 5-HV production through the flask and batch cultivations, and YahK was determined to be the most appropriate aldehyde reductase. Further modification to enhance 5-HV production was investigated by deletion of an endogenous gabD gene responsible for the oxidation of glutarate semialdehyde into glutaric acid in order to suppress glutaric acid by-production. Finally, 52.1 g/L 5-HV with the yield of 0.33 g/g glucose was achieved by fed-batch fermentation of the engineered C. glutamicum with overexpression of davTBA genes and the yahK gene along with gabD deletion in the chromosome.

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Cadaverine is a C5 diamine monomer used for the production of bio-based polyamide 510. Cadaverine is produced by the decarboxylation of l-lysine using a lysine decarboxylase (LDC). In this study, we developed recombinant Escherichia coli strains for the expression of LDC from Hafnia alvei. The resulting recombinant XBHaLDC strain was used as a whole cell biocatalyst for the high-level bioconversion of l-lysine into cadaverine without the supplementation of isopropyl β-d-1-thiogalactopyranoside (IPTG) for the induction of protein expression and pyridoxal phosphate (PLP), a key cofactor for an LDC reaction. The comparison of results from enzyme characterization of E. coli and H. alvei LDC revealed that H. alvei LDC exhibited greater bioconversion ability than E. coli LDC due to higher levels of protein expression in all cellular fractions and a higher specific activity at 37 °C (1825 U/mg protein > 1003 U/mg protein). The recombinant XBHaLDC and XBEcLDC strains were constructed for the high-level production of cadaverine. Recombinant XBHaLDC produced a 1.3-fold higher titer of cadaverine (6.1 g/L) than the XBEcLDC strain (4.8 g/L) from 10 g/L of l-lysine. Furthermore, XBHaLDC, concentrated to an optical density (OD600) of 50, efficiently produced 136 g/L of cadaverine from 200 g/L of l-lysine (97% molar yield) via an IPTG- and PLP-free whole cell bioconversion reaction. Cadaverine synthesized via a whole cell biocatalyst reaction using XBHaLDC was purified to polymer grade, and purified cadaverine was successfully used for the synthesis of polyamide 510. In conclusion, an IPTG- and PLP-free whole cell bioconversion process of l-lysine into cadaverine, using recombinant XBHaLDC, was successfully utilized for the production of bio-based polyamide 510, which has physical and thermal properties similar to polyamide 510 synthesized from chemical-grade cadaverine.