Ecology of plastic-degrading microorganisms from an abandoned landfill site

Polyethylene (PE) is the most common petroleum-based plastic. It accumulates at a rate of several millions of tons per year since its recalcitrance to both biotic and abiotic degradation. Despite these difficulties, recent evidences showed that some microbial strains can partially degrade PE pre-oxidized by abiotic processes. Here, we investigated plastic samples from an abandoned landfill, with the aim of elucidating the ecology of soil microorganisms able to grow on the plastics and to correlate them with plastic degradation levels. Microbial DNA derived from the plastic surfaces, the landfill soil and an uncontaminated neighboring agricultural soil was analyzed by Illumina high-throughput sequencing of 16S rRNA amplicons. A first isolation was carried after detachment of the biofilm from the plastic surfaces and serial dilutions on selective agar plates of mineral medium with paraffin as the only carbon source. The analysis on total microbial community through Illumina 16S rRNA sequencing shows that different PE samples host different species. This confirms the results from differential scanning calorimetric analysis of the material that shows an additional shoulder melting peak with various enthalpies besides the main melting peak, implying the plastic exhibited different degrees of degradation, suggesting that plastics seems to be able to select microbiological activity that correlates with PE degradation level. Interestingly, the microbial population derived from plastic sample with the highest degradation level is very similar to that of the soil derived from contaminated landfill. The first cultured selection based on the ability to grow on paraffin of the microbial community derived from the biofilm on plastics surfaces allows us to identify by RAPD (Random Amplified Polymorphic DNA) analysis a total of 49 different strains. The most representative are Bacillus genus with 12 different species represented, followed by Pseudomonas, Lysinibacillus, Comanomonas and Acinetobacter. The study represents one of the first fine scale assessment of microorganisms growing on plastics from a landfill site, and the strains with the best degradation abilities results will be further exploited for remediation purposes.