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Synergistic Remediation of Microplastics-Contaminated Soil by Immobilized Laccase and Pseudomonas putida: Insights into Microbial Activity, Soil Enzymatic, and Molecular Responses in Maize (Zea Mays L.)
Summary
A greenhouse pot experiment showed that combining immobilized laccase enzyme with the bacterium Pseudomonas putida degraded up to 21.38% of soil microplastics over 60 days while improving microbial diversity and maize growth compared to untreated controls. This bioremediation approach offers a promising, ecologically compatible strategy for cleaning microplastic-contaminated agricultural soils and restoring their fertility and food safety.
The emergence of microplastics (MPs) as pollutants in agricultural soils is increasingly alarming, presenting significant toxic threats to soil ecosystems. This study aimed to evaluate the synergistic efficacy of immobilized laccase enzyme and the rhizobacterium Pseudomonas putida in degrading soil-borne microplastics and improving soil quality, microbial diversity, and physiological performance of maize (Zea mays L.). A pot experiment was conducted using agricultural soil artificially contaminated with microplastics. Treatments included: control (no MPs), MPs only, MPs with P. putida, MPs with immobilized laccase, and MPs treated with combined laccase and P. putida. The experiment was conducted for 60 days under controlled greenhouse conditions. After the experimental period, comprehensive analyses were carried out to assess soil quality, microbial diversity, and plant physiological parameters. Results from the present study showed that the combined application of immobilized laccase and P. putida significantly enhanced the degradation of soil-borne MPs, with degradation rates reaching up to 21.38 ± 1.07%, compared to negligible degradation in the microplastics-only treatment. Laccase activity increased to 4.07 ± 0.20 U g⁻¹ soil, and dehydrogenase activity reached 127.21 ± 6.36 µg triphenyl formazan g⁻¹ day⁻¹. Microbial biomass carbon was elevated to 248.85 ± 12.44 µg/g, while microbial diversity also increased (Shannon Index: 2.95 ± 0.15). Z. mays grown in the combined treatment exhibited improved shoot (12.13 ± 0.61 g) and root fresh weight (6.37 ± 0.32 g). Photosynthetic parameters also improved, including chlorophyll a content (1.52 ± 0.08 mg g⁻¹ FW) and net photosynthesis rate (14.64 ± 0.73 µmol carbon dioxide m⁻² s⁻¹). Additionally, organic acid profiling showed elevated levels of oxalic and citric acids in root exudates under the combined treatment. Research findings, therefore, suggested that the combined application of immobilized laccase and P. putida can enhance MPs degradation in soil and improve plant growth and soil health, as reflected by increased microbial activity and balanced organic acid exudation.