Polyethylene biotransformation by an earthworm gut-derived Streptomyces sp.: insights into microenvironment-associated metabolism

Polyethylene (PE) is a highly recalcitrant polymer that resists microbial degradation owing to its hydrophobic and chemically inert structure. In this study, a Streptomyces sp. strain MH-1, isolated from the earthworm gut, was investigated for its interaction with PE under carbon-limited conditions. The strain was associated with approximately 15% reduction in PE weight after 30 days of incubation. Fourier transform infrared (FTIR) analysis revealed alterations in polymer chemistry, including a reduction in the carbonyl peak (approx. 1715 cm‒1) and a decrease in the carbonyl index from 0.19 in the control to 0.10 in treated samples. In silico analysis using a closely related Streptomyces genome as a reference framework identified putative genes associated with hydrocarbon metabolism and suggested potential oxidative and assimilatory pathways. Candidate aldehyde dehydrogenases, including bifunctional alcohol/aldehyde dehydrogenase (adhE), together with genes associated with fatty acid metabolism and β-oxidation, may indicate potential mechanisms involved in the processing of oxidation intermediates. These findings, combined with biofilm formation and growth under confined conditions, highlight the importance of PE-associated microenvironments and provide a basis for exploring microbial adaptation and potential metabolic processes involved in PE biotransformation.