Inverse Relationship Between Microplastic Abundance and Microplastic Biodegradation Potential in Soils from Both Natural and Anthropogenic Sites in Lithuania

Biodegradation is a sustainable strategy for removing microplastics (MP), owing to its environmental compatibility and cost-effectiveness. This study investigated MP distribution, characterized microbial communities, and assessed the presence of plastic-degradation-associated genes across three locations in Lithuania: an operating Kazokiškės landfill, a closed Kariotiškės landfill, and a natural grassland. Polyamide was the most abundant plastic across all locations, followed by polyethylene, with the highest MP concentrations detected in the operating landfill. Sequencing of 16S rRNA and ITS genes revealed site-specific microbial communities with significantly different β-diversity. Operating landfill soils were enriched in plastic-associated genera, including Methylocaldum, Rhizobium, Brevundimonas, Aspergillus, and Malassezia. Based on the microbiome analysis, both studied landfills had distinct communities yet shared some plastic-degradation-associated genera. The key novel finding is contrary to conventional assumptions: the active landfill had the most MP and the highest number of plastic-associated microbial genera, yet the narrowest range of plastic-degradation-associated genes was limited to alkane hydroxylases and styrene monooxygenases, possibly due to suppression by constant input of fresh, labile organic waste. The grassland and closed landfill, despite lower MP abundance, hosted a broader diversity of studied genes: cutinases in both and urethanases exclusively in the grassland, suggesting broader plastic polymer utilization potential in non-operating landfill soils. These findings suggest that ordinary and closed-landfill soils are an underappreciated reservoir of plastic-degradation potential, and that the closed-landfill topsoil microbiome may be influenced by buried waste beneath it.