The durability of plastics is desirable for many applications. However, it also causes improperly disposed plastics to persist in nature and accumulate in many environments and organisms. In recent years, only 20% of global plastic waste has been recycled, and the majority (55%) has been discarded in either landfills or the natural environment. This calls for the exploration of new ways to break down and recycle plastic waste.
Utilising plastic degrading microbes is a promising approach as several microbial taxa and enzymes have been associated with plastic degradation. In this study, we aimed to identify differentially abundant microbes on plastics and their encoded enzymes with plastic degrading potential.
To achieve our goals, we used a combination of microscopic and spectroscopic analyses and a culture-independent microbial exploration via metagenomics. Virgin and weathered polyethylene, polypropylene and polystyrene nurdles were incubated in seawater for 35 days. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were used to visualise microbial settlement on the plastics and changes in plastic surface chemistry. DNA extracted from the plastics and glass controls was used for metagenomics.
SEM images confirmed that microbes were able to settle on plastics during the incubation period. Changes in plastic surface chemistry, especially the increase in carbonyl bonds, suggest that microbes may be able to attack the long chain polymer by introducing carbonyl groups, which can be further degraded and used as carbon source. Preliminary results from the metagenomic analysis revealed diverse microbial communities growing on plastics, with specific lineages showing significantly differentially abundances for certain plastic types.
Our next steps are to reconstruct metagenome-assembled genomes (MAGs) and to detect potential plastic degrading enzymes in assemblies and MAGs. These encoded enzymes can be validated in subsequent studies, and potentially incorporated into advanced bio-recycling. This approach would allow us to break down plastic waste and bio-upcycle the depolymerised products into higher-value building blocks and move us one step closer towards a circular economy.