Seung Hoon Choi’s research while affiliated with Korea Research Institute of Bioscience and Biotechnology and other places

Polyurethane (PU), currently replacing existing synthetic materials worldwide, is a synthetic polymer derived from polyols, isocyanates, and a chain extender added by condensation reactions. PU wastes which are difficult to recycle, are commonly discarded in landfills and flow into ecosystems, thereby causing serious environmental problems. In recent years, insect-associated microbes have become a promising, eco-friendly strategy as an alternative to plastic recycling. This study aimed to evaluate the potential of Serratia sp. HY-72 strain isolated from the intestine of the Asian mantis (Hierodula patellifera) for PU degradation. The 65 kDa family I.3 lipase which degrades PU was identified and characterized, with a specific activity of 2,883 U mg−1. The bacterial filtrates and the recombinant lipase degraded Impranil (a colloidal polyester-PU dispersion, 100 g l−1) by 85.24 and 78.35% after 72 h incubation, respectively. Fourier transform infrared spectroscopy analysis revealed changes in Impranil functional groups, with decreased C=O functional group and aliphatic chain signals, and increased N-H bending with C-N stretching and C-O stretching. The current study also revealed that the HY-72 strain biodegraded the commercial PU foams (polyester- and polyether- PU) with 23.95 and 10.95% weight loss after 2 weeks, respectively with changes in surface morphology and structure such as cracks, roughness, and surface roughening. Altogether, this is one of the few studies reporting biodegradation of PU by the insect-associated microbe. These findings suggest that the insect-associated microbe could be a promising resource for biodegradation and recycling of plastic waste.

In this study, we evaluated the effects of the Xanthomonas sp. HY-71 strain isolated from the intestine of a Japanese carpenter bee (Xylocopa appendiculata), on polyurethane (PU) degradation and bioconversion. The abilities of the strain to degrade polyacrylic-, polyester-, and polyether-based PU were characterized by weight loss measurement, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM), and chemical composition analysis. The cell-free filtrates of the strain showed 88.12% of acryl PU-Siegel degradation rates (100 mg/mL) within 3 days. FTIR spectroscopy revealed changes in functional groups, with decreased C=O (1725 cm ⁻¹) and aliphatic chain signals (704 cm ⁻¹) and increased N-H stretching (3314 cm ⁻¹), N-H bending with C-N stretching (1524 cm ⁻¹), C-O-C stretching (1040 cm ⁻¹), and C-N stretching (1226 cm ⁻¹). Polyester-PU and polyether-PU foams, respectively, lost 23.95% and 10.95% of their weight after 2 weeks. SEM revealed surface morphology and structural changes such as holes, cracks, roughness, and grooves. In addition, the bioconversion capability of HY-71 using PU as a nutritional source was also demonstrated by monitoring the exopolysaccharide production yield in the presence of PU foam. The exopolysaccharide yields with acryl PU-Siegel and PS-PU foam (24.6 g/L and 22.6 g/L, respectively) were significantly higher than those of the control and polyether-PU treatments. This study is the first on the insect gut microbe Xanthomonas sp. HY-71 strain, which has PU degradation capability, and provides insight into the potential applications of insect-related bacteria in plastic waste management.