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Kinetics and Potential Mechanisms of LDPE and PBAT Microplastics Biodeterioration by Soil Bacteria Bacillus cereus L6
Summary
Scientists isolated a strain of Bacillus cereus from long-term microplastic-contaminated agricultural soil and found it could cause measurable mass loss in both LDPE (0.99% over 28 days) and biodegradable PBAT (3.58% over 28 days) agricultural film microplastics, with genome sequencing revealing the biochemical pathways involved. The faster degradation of PBAT confirms its greater biodegradability, while the LDPE results suggest even conventional polyethylene films can be partially broken down by native soil bacteria. These findings have implications for understanding how microplastics from agricultural films persist in or are gradually processed within soil ecosystems.
Low-density polyethylene (LDPE) and poly (butylene adipate-co-terephthalate) (PBAT) agricultural films are major components of microplastics (MPs) and their contamination in agriculture due to their difficulty to recycle. However, potential degradation mechanisms of MPs from LDPE and PBAT in agricultural soils are still unclear. Here, we isolated a strain of Bacillus cereus L6 from long-term agricultural MP-contaminated soil and analyzed its potential biochemical pathways involved in LDPE and PBAT turnover through functional prediction from shotgun genome sequencing. After 28 days of incubation with MPs, Bacillus cereus L6 caused a net mass loss of 0.99% LDPE-MPs/28 days and 3.58% PBAT-MPs/28 days. The surfaces of LDPE and PBAT degraded in bioassays added with Bacillus cereus L6 showed wrinkles, cracks, and pits, accompanied by an increase in roughness. The crystallinity and thermal stability of both LDPE- and PBAT-MPs were decreased and the hydrophobicity of PBAT-MPs was reduced. Whole-genome sequencing analysis showed that Bacillus cereus L6 potentially encoded genes for enzymes related to the biodeterioration of additives in LDPE and PBAT. Moreover, genomic CAZymes predictive analysis showed that genes related to oxygenases and lyases were annotated in the strain L6 Auxiliary Activities family. These findings offer a theoretical foundation for deeper exploration into the degradation and metabolic processes of MPs from discarded agricultural plastics in the environment.