Aerobic biodegradation of untreated polyester-polyether urethanes by newly isolated yeast strains Exophilia sp. NS-7 and Rhodotorula sp. NS-12

Polyester-urethanes as the most widely used polyurethanes (PUs) are among the most recalcitrant plastics in natural conditions. Among existing approaches for managing and reducing plastic waste, biodegradation as a promising approach to reduce plastic waste pollution has drawn scientific society's attention in recent years. In this study, two polyester- polyether urethane degrading yeasts were isolated and identified as two new strains of Exophilia sp. NS-7 and Rhodotorula sp. NS-12. The results showed that Exophilia sp. NS-7 is esterase, protease, and urease positive, and Rhodotorula sp. NS-12 can produce esterase and urease. Both strains can degrade -Impranil (R) as the sole carbon source with the highest growth rate in 4-6 and 8-12 days, respectively. SEM micrograph revealed PU degradation ability in both strains by showing so many pits and holes in treated films. The Sturm test showed that these two isolates can mineralize PU to CO2, and significant decreases in N-H stretching, C-H stretching, C=O stretching, and N-H/C=O bending absorption in the molecular structure of PU were revealed by the FT-IR spectrum. The detection of the deshielding effect in chemical shifts of the H-NMR spectrum after the treatment also confirmed the destructive effects of both strains on PU films.

Automated summary

Polyester-urethanes, widely used polyurethanes, are very difficult to degrade in natural conditions. Biodegradation has become a promising approach to reduce plastic waste pollution, and in this study, two new strains of Exophilia sp. NS-7 and Rhodotorula sp. NS-12 were identified as capable of degrading polyester-polyether urethane. These strains showed positive esterase and urease activities, and could degrade -Impranil (R) within 4-6 and 8-12 days, respectively. They also exhibited PU degradation ability through the formation of pits and holes on treated films. The Sturm test and FT-IR spectrum confirmed the mineralization of PU to CO2 and changes in molecular structure, respectively, while the NMR spectrum showed destructive effects on PU films.