Effective microbial formulations using sustainable carriers for the remediation of plastic-affected soils

The increasing use of mulching films in intensive agriculture, together with their inefficient end-of-life disposal, has led to a significant plastic accumulation in soils, which contributes to disrupting ecosystems. The aim of this work was to determine the ability of different sustainable carriers to harbor and introduce plastic-degrading microorganisms into contaminated soils to provide a biotechnological tool that potentially enhances plastic decontamination, ameliorating the harmful effect of this type of pollutant in soil. To this end, pure cultures and co-cultures of Bacillus subtilis and Pseudomonas alloputida (specialized plastic-degrading strains) were added to three sustainable carriers (vermicompost, biochar, and calcium alginate beads) for the preparation of microbial formulations. After a storage period, the maintenance of cell viability and enzymatic activities related to the bioremediation potential of plastic materials of the inocula tested in the different microbial formulations (carrier + inoculant) were evaluated. The effectiveness of the formulations for plastic mineralization was tested by measuring CO2 emissions after two months. The results showed that biochar, followed by vermicompost, favored greater microbial survival (107 CFU g-1), while alginate formulations showed variable cell viability results, from 107 to 104 CFU g-1. Biochar also excelled in maintaining enzymatic activities related to plastic degradation, achieving the expression of 100% of the tested enzymes. Additionally, biochar-based formulations applied to soils contaminated with LLDPE plastic showed the highest mineralization rates, with statistically significant differences compared to the plastic-free control. These results lay the foundation for the development of new plastic decontamination technologies paving the way for the sustainable treatment of polluting and recalcitrant materials such as plastic.