The aim of this work was to establish and analyze stable microbial consortia for the degradation of a mixture of polyethylene, polypropylene, and nylon. A complex environmental inoculum from landfills and wastewater treatment plants was used as the starting material. The consortia were enriched over a four-month period in minimal medium with microplastics as the main carbon source, following two parallel strategies: natural enrichment and bioaugmentation with nineteen fungal strains. Microbial community dynamics were monitored using high-throughput amplicon sequencing of 16S, 18S, and ITS taxonomic markers. The results showed a drastic decline in alpha diversity and a radical shift in beta diversity, confirming the formation of a specialized plastisphere. Bioaugmentation significantly stabilized the consortium, with the genera Penicillium and Aspergillus becoming dominant and outcompeting other eukaryotes. PERMANOVA results confirmed that microplastics act as the primary selective factor driving the development of a unique bacterial community, while fungi serve as a stabilizing factor that maintains a higher number of low-abundance amplicon sequence variants (ASVs). A total loss of methanogenic archaea was observed in line with their functional insignificance in aerobic degradation systems. This research demonstrates that cross-kingdom synergy in bioaugmented consortia creates structurally mature and reproducible systems, which is important for developing biotechnological processes for plastic waste bioremediation.
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