Ecological distribution and functional characterization of polyethylene-degrading enzymes from diverse metagenomes.

Polyethylene (PE), the most widely produced synthetic polymer, is highly resistant to degradation and poses long-term ecological risks due to its accumulation in terrestrial and aquatic ecosystems. Although biological degradation pathways have been investigated, research has primarily concentrated on heavily polluted environments, leaving the ecological distribution of PE-degrading enzymes largely unknown. In this study, we systematically screened more than 4.57 billion metagenomic sequences from diverse ecological sources-including farmland soils, Przewalski's horse gut microbiota, insect symbionts, and human oral microbiomes-for homologs of known PE-degrading enzymes. A total of 701 candidate sequences were identified using an integrated pipeline combining sequence homology, structural modeling, and molecular docking. Thirty-two representative enzymes were heterologously expressed and tested on pristine PE films and microspheres, among which 25 exhibited measurable activity, inducing surface erosion, up to ∼1.5% mass loss (w/w) of PE films over 30 days, and oxidative modifications. These degradative effects were validated by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and stable carbon isotope (δC) analysis, collectively supporting molecular-level oxidation and early-stage carbon turnover associated with enzymatic PE degradation. Notably, PE-degrading activity was observed in microbiomes from relatively minimally disturbed environments, suggesting that microbial communities may adaptively evolve plastic-degrading capabilities in response to chronic, low-level exposure. These findings expand our understanding of plastic pollution's ecological footprint and highlight naturally occurring enzymes as promising candidates for sustainable bioremediation.