Co-application of organic amendment and plastic-degrading microbial inoculum drives functional microbial shifts in plastic-contaminated soils

Plastic contamination in soil poses a significant threat to ecosystem health, disrupting soil properties and compromising agricultural sustainability. This study explores a novel bioremediation strategy for plastic-contaminated soil, utilizing a carrier to inoculate a specialized plastic-degrading microbial consortium. Mesocosm experiments were conducted in 4 L containers with 2.8 kg soils amended with three types of plastics—low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and naturally weathered mulching film, at a concentration of 0.036 % (w/w)—under both inoculated and non-inoculated conditions. The microbial consortium, comprised of Bacillus subtilis RBM2 and Pseudomonas putida REBP7, was delivered via an organic-mineral blend of vermicompost, biochar (pH 8.50), and urea, aiming to promote its stable incorporation and persistence in the soil (15 % moisture). Viable cell counts using selective culture media and qPCR-based quantification confirmed that inoculated strains not only persisted but also, in some cases, thrived in the presence of plastic contaminants. Metabarcoding analysis of the soil microbiome revealed shifts in community composition and diversity, with specific enrichment of genera associated with plastic degradation. Furthermore, the upregulation of key enzymatic activities related to alkane degradation—such as alkane 1-monooxygenase—highlighted the functional activation of xenobiotic degradation pathways in response to both the inoculum and plastic exposure. Overall, the results demonstrate that the integration of a plastic-degrading microbial consortium via organic amendment can mitigate the adverse impacts of plastic pollution by restoring soil microbial functions and enhancing biodegradation potential. This sustainable approach offers a promising tool for managing plastic contamination in agricultural soils while supporting circular economy principles and long-term soil health.