Set of Small Molecule Polyurethane (PU) Model Substrates: Ecotoxicity Evaluation and Identification of PU Degrading Biocatalysts

Abstract

Polyurethanes (PUs) are an exceedingly heterogeneous group of plastic polymers, widely used in a variety of industries from construction to medical implants. In the past decades, we have witnessed the accumulation of PU waste and its detrimental environmental impacts. PUs have been identified as one of the most toxic polymers leaching hazardous compounds derived both from the polymer itself and the additives used in production. Further environmental impact assessment, identification and characterization of substances derived from PU materials and establishing efficient degradation strategies are crucial. Thus, a selection of eight synthetic model compounds which represent partial PU hydrolysis products were synthesized and characterized both in terms of toxicity and suitability to be used as substrates for the identification of novel biocatalysts for PU biodegradation. Overall, the compounds exhibited low in vitro cytotoxicity against a healthy human fibroblast cell line and virtually no toxic effect on the nematode Caenorhabditis elegans up to 500 µg ml−1, and two of the substrates showed moderate aquatic ecotoxicity with EC50 values 53 µg ml−1 and 45 µg ml−1, respectively, on Aliivibrio fischeri. The compounds were successfully applied to study the mechanism of ester and urethane bond cleaving preference of known plastic-degrading enzymes and were used to single out a novel PU-degrading biocatalyst, Amycolatopsis mediterranei ISP5501, among 220 microbial strains. A. mediterranei ISP5501 can also degrade commercially available polyether and polyester PU materials, reducing the average molecular number of the polymer up to 13.5%. This study uncovered a biocatalyst capable of degrading different types of PUs and identified potential enzymes responsible as a key step in developing biotechnological process for PU waste treatment options.

Rapid biodegradation of microplastics generated from bio-based thermoplastic polyurethane

“…2b cleaves this bond to further catabolize the remaining compound. Previous work with other polyester-polyurethane degrading bacteria has indicated that depolymerization can occur in a stepwise fashion with ester bonds being initially hydrolyzed followed by urethane bonds 23 – 25 . Furthermore, a urethane-bond cleaving enzyme found in Rhodococcus equi TB-60 was found to be inducible by the presence of amide bond containing compounds 17 .…”

XTT assay for detection of bacterial metabolic activity in water-based polyester polyurethane

“…Screening for PU degradation using agar plate-based methods is widely used and has allowed the identification of bacterial strains with high degrading activity [ 8 , 39 , 40 ]. However, a negative phenotype in agar plate screening does not necessarily indicate the absence of PU-degrading activity.…”

Designing biodegradable alternatives to commodity polymers

“…This urethane-degrading strain was found to act on polyether and polyether-based polyurethanes, with a reduction of up to 13.5% in the number average molecular weight of the polymer. 174 Some cutinases, lipases and carboxylesterases have been found to act on the soft segments of ester-based polyurethanes, but as yet no enzymes which cleave ether linkages have been reported. Bhavsar et al have discussed the challenges associated with biodegradation of polyurethanes, and evaluates the potential of employing bacteria and fungi to accelerate biodegradation.…”