Microbial networks and soil properties influence surface biodegradation of polyethylene terephthalate (PET) and...

Plastic accumulation in terrestrial environments poses increasing ecological and public health risks, yet the mechanisms driving plastic biodegradation in soils remain poorly understood. Here, we investigated the 300-day degradation of polyethylene terephthalate (PET) and polylactic acid (PLA) in soil microcosms derived from 16 environmentally diverse soils. Plastic surface transformation was monitored using Fourier Transform Infrared (FTIR) spectroscopy and water contact angle (CA) measurements, while microbial community shifts and interactions were assessed through 16S rRNA sequencing and co-occurrence network analyses. Both polymers exhibited measurable surface degradation, with PET and PLA showing up to 38% and 36% reductions in carbonyl index, respectively, and hydrophobicity decreases of 52% (PET) and 26% (PLA). Furthermore, plastic exposure significantly altered microbial composition and network topology. For instance, PET networks were enriched with known degraders (Bacillus, Burkholderia, Pseudomonas) and opportunistic taxa (Salmonella, Escherichia), while PLA networks contained microorganisms with broader metabolic abilities, including Gemmata, Acidicapsa, and Methylocystis. Canonical correlation and regression analyses revealed that pH, carbonate content, conductivity, and nutrient ions, such as K⁺, Mg²⁺, and S²⁻ were the strongest predictors of biodegradation extent. Alkaline, carbonate-rich soils with elevated conductivity supported the greatest polymer transformation. These findings demonstrate that soil plastic biodegradation is a network-driven, environmentally modulated process in which geochemical parameters and microbial consortia jointly determine degradation potential. Understanding these coupled biogeochemical mechanisms provides a framework for optimizing in situ bioremediation of plastic-contaminated soils.