Biotransformation of ethylene glycol to glycolic acid by Yarrowia lipolytica: A route for poly(ethylene terephthalate) (PET) upcycling

Abstract

Biological recycling of PET waste has been extensively investigated recently to tackle plastic waste pollution, and ethylene glycol (EG) is one of the main building blocks recovered from this process. Wild-type Yarrowia lipolytica IMUFRJ 50682 can be a biocatalyst to biodepolymerize PET. Herein, we report its ability to perform oxidative biotransformation of EG into glycolic acid (GA): a higher value-added chemical with varied industrial applications. We found that this yeast tolerates high EG concentrations (up to 2 M) based on maximum non-inhibitory concentration (MNIC) tests.Whole-cell biotransformation assays using resting yeast cells showed GA production uncoupled to cell growth metabolism, and 13 C nuclear magnetic resonance (NMR) analysis confirmed GA production. Moreover, higher agitation speed (450 vs. 350 rpm) resulted in a 1.12-fold GA production improvement (from 352 to 429.5 mM) during Y. lipolytica cultivation in bioreactors after 72 h. GA was constantly accumulated in the medium, suggesting that this yeast may also share an incomplete oxidation pathway (i.e., it is not metabolized to carbon dioxide) as seen in acetic acid bacterial group.Additional assays using higher chain-length diols (1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol) revealed that C4 and C6 diols were more cytotoxic, suggesting that they underwent different pathways in the cells. We found that this yeast consumed extensively all these diols, however, 13 C NMR analysis from supernatant identified solely the presence of 4-hydroxybutanoic acid from 1,4-butanediol, along with GA from EG oxidation. Findings reported herein reveal a potential route for PET upcycling to a higher value-added product.

From trash to cash: current strategies for bio-upcycling of recaptured monomeric building blocks from poly(ethylene terephthalate) (PET) waste

“…150 On the other hand, Kim et al used chemoenzymatic hydrolysis technology to obtain EG (30.6 g L −1 ) from PET, which was subsequently converted to 31.4 g L −1 of GA with a molar yield of 91.6% for G. oxydans. Carniel et al 233 demonstrated the ability of Y. lipolytica strain IMUFRJ 50682 to biotransform reagent-grade EG into GA (430 mM), at a molar yield of 78.1% after 72 h. This yeast is also capable to biodepolymerize PET, 216 so EG released in this process could be concomitantly converted into GA by the same biocatalyst.…”

“…To the best of our knowledge, only the bacterium I. sakainesis ( produces PHA) and yeast Y. lipolytica ( produces GA) have been reported with this ability so far. 125,233 Thus, synthetic biology is a crucial tool to diversify the variety of final products, by constructing metabolic pathways containing specific enzymes from different organism sources to catalyze sequential reactions. The choice of microbial chassis for expressing these metabolic pathways must take into account several factors: source of heterologous enzymes, monomer uptake capability, and tolerance to moderate to high monomer and product concentrations, inability to consume final product, among others.…”

“…It is worth to highlight that PET monomers can also be cytotoxic to the microbial chassis, and few studies have investigated this effect in depth. 233 Limiting monomer concentrations in the fermentation will consequently reduce product productivity, leading to lower financial gain per batch. In parallel, products can similarly affect microorganisms, so it is important to understand these factors in conjugation.…”

“…Carniel et al 233 demonstrated the ability of Y. lipolytica strain IMUFRJ 50682 to biotransform reagent-grade EG into GA (430 mM), at a molar yield of 78.1% after 72 h. This yeast is also capable to biodepolymerize PET, 216 so EG released in this process could be concomitantly converted into GA by the same biocatalyst.…”

CYP116B5‐SOX: An artificial peroxygenase for drug metabolites production and bioremediation

“…In order to study the applicability of the fusion enzyme catalysis in bioremediation we performed a reaction scale-up exploiting a strain of E. coli BL21 (DE3) cells transformed with the pET-28-a-CYP116B5-SOX(+) vector: E. coli (CYP116B5-SOX). We employed the transformed bacteria as biocatalytic system to remove tamoxifen, [64][65][66][67][68][69][70][71][72][73] commonly reported as water pollutant, [9] from an aqueous buffered medium, taken as a model of contaminated water. We used HPLC-MS to identify the metabolites produced by CYP116B5-SOX catalysis.…”