Microenvironment of Landfill-Mined Soil-Like Fractions (LMSF): Evaluating the Polymer Composting Potential Using Metagenomics and Geoenvironmental Characterization

The search for potent plastic-degrading bacteria has been a focal point of research over the recent decades to develop sustainable methods for plastic waste management. Despite promising results at the laboratory scale, replicating the same at the field scale has been limited. Natural extremophilic conditions of the landfill host many plastic-degrading bacteria, and recently, culture-independent Next-Generation Sequencing metagenomics approaches are being adopted to screen them and exploit their utilities. However, one of the main challenges is the difficulty in designing the optimum artificial test conditions for understanding the growth and metabolic activities of the concerned microorganisms. In the current study using precision metagenomics, genes coding for PET and PHA degrading enzymes were screened from a landfill-mined soil-like fraction (LMSF) sample, with landfill soil under a freshly deposited waste dump acting as the control. Subsequently, thorough geoenvironmental characterization of the samples was performed to generate an understanding of the growth conditions of the microorganisms. Genes encoding for MHETase outpopulated the genes encoding for PETase in LMSF, while the reverse trend was observed in the control. The abundance and taxonomic distribution of the hosts containing genes of PETase and MHETase enzymes in the samples, when co-related with the FTIR spectra of the samples, indicated that the PET residues might have possibly degraded to MHET under natural conditions. Usually, commercial composts, which are already a market-ready product for the agriculture sector, are used for polymer composting, which is not sustainable in the long run. The structural and functional patterns of the microbes obtained in the metagenomics study and permissible levels of leachable heavy metals generate promise for the landfill-mined soil-like fractions to be potentially used for polymer degradation. Alongside this, the presence of a monotypic oceanic genus Plesiocystis in the landfill environment was confirmed, which is of utmost importance to the field of microbial ecology.