Biodegradation of polypropylene by Bacillus cereus PP-5 isolated from waste landfill

Waste polypropylene (PP) plastic has caused serious environmental pollution, and biological methods provide a feasible strategy to deal with the environmental pollution and resource waste caused by waste plastics. In this study, we investigated the physicochemical and structural changes of PP plastic degraded by Bacillus cereus PP-5, which was isolated from a waste landfill. After 30-day incubation with PP-5, structural properties of PP powder were analyzed using high-temperature gel permeation chromatography, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, and differential scanning calorimetry. We found that PP-5 colonized the plastic surface through biofilm, and the bio-deterioration with visible cracks was also observed from the PP surfaces, the carbonyl index of PP-5-treated PP powder was identified as 0.536. Meantime, the weight-average molecular weight and thermal stability of PP decreased, while melting enthalpy and average crystallinity increased after PP-5treatment. Moreover, oxidative cleavage of carbon-carbon bonds of PP was observed from the appearance of quaternary carbon and elevated CO groups of PP-5-treated PP plastics, suggesting microbial oxidation. Our findings elucidate a potential bio-oxidizing mechanism for microbial-driven PP degradation, and also highlight the application prospects in bio-recycling systems, particularly for managing plastic waste in landfills or marine environments.