Selective colonization processes of plastic-loving bacteria in an abandoned landfill site

Polyethylene (PE), the most common petroleum-based plastic, is strongly recalcitrant to degradation. Despite this, recent evidences showed that a few 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. Isolations were carried after detachment of the biofilm from the plastic surfaces and se- rial dilutions on selective agar plates of mineral medium with paraffin as the only carbon source. Microbial DNA derived from the plastic surfaces, the landfill soil and an uncontam- inated neighboring agricultural soil was also analyzed by Illumina sequencing of 16S rRNA amplicons. A total of 49 strains growing on paraffin were identified: the most representative genus is Bacillus genus with 12 different species represented, followed by Pseudomonas, Lysini- bacillus, Comanomonas and Acinetobacter. Differential scanning calorimetric analysis of the plastic samples showed an additional shoul- der melting peak with various enthalpies besides the main melting peak, implying the plastic exhibited different degrees of degradation. In parallel, Illumina 16S rRNA analyses showed that the different plastics hosted different microbial communities, and that the bacterial community derived from plastic sample with the highest degradation level was the most similar to that of the soil derived from contaminated landfill. Results point to an interesting correlation between the level of plastic degradation and the composition of the microbial biofilm.