Discovery and characterization of novel polyacrylic urethane-degrading bacteria from intestine of the red-veined darter (Sympetrum fonscolombii)

Plastic waste accumulation poses significant environmental and socioeconomic challenges due to the inherent resistance of plastics to degradation. Among plastics, polyurethane (PU) is widely used but particularly recalcitrant. In this study, we identified and characterized two bacterial strains, Serratia sp. IBT73 and Pseudomonas sp. IBT82 from the intestine of a Red-veined Darter (Sympetrum fonscolombii), with the potential to degrade polyacrylic-urethane (PAU). Extracellular esterase, urease, and protease activities involved in PU degradation were detected and purified esterases from both strains exhibited PAU-degrading capabilities. The biodegradation of PU materials was comprehensively confirmed through scanning electron microscopy, Fourier-transform infrared spectroscopy, and chemical analysis of degradation products. Quantitative analysis showed that the strains degraded the PU foams, with up to 10.05 % degradation of PS-PU by IBT73 and 6.81 % by IBT82, while PE-PU degradation reached 3.23 % and 4.33 %, respectively. The purified esterases showed even higher activity, achieving 89.76 % (from IBT73) and 73.21 % (from IBT82) degradation of a PAU suspension within 48 h. Transcriptome analysis revealed distinct transcriptional responses: IBT73 strain enhanced small molecule metabolic pathways, while IBT82 strain activated stress response pathways under PAU exposure. Structural analysis and metabolite identification suggested cleavage of urethane, ester, and aromatic structures, supporting active microbial degradation. These findings highlight the broad degradation potential of insect gut microbes IBT73 and IBT82 across chemically diverse PU materials, suggesting their applicability for sustainable PU waste management.