Kinetics and Potential Mechanisms of LDPE and PBAT Microplastics Biodeterioration by Soil Bacteria Bacillus cereus L6

TL;DR

A soil bacterium, Bacillus cereus L6, can degrade LDPE and PBAT microplastics, causing physical and chemical changes that suggest potential environmental cleanup applications.

Contribution

Identification of a soil bacterium capable of degrading LDPE and PBAT microplastics with insights into its potential enzymatic mechanisms.

Findings

Bacillus cereus L6 caused a 0.99% mass loss of LDPE-MPs and 3.58% mass loss of PBAT-MPs over 28 days.

Degradation of LDPE and PBAT by Bacillus cereus L6 resulted in surface wrinkling, cracking, and increased roughness.

Genomic analysis revealed potential oxygenase and lyase genes linked to microplastic degradation in Bacillus cereus L6.

Abstract

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.

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