Synergistic effect of styrofoam fed mealworm gut bacterial strain Priestia megaterium RP1/S1 and organic amendments enhances LDPE biodegradation in soil.

The increasing accumulation of low-density polyethylene (LDPE) in terrestrial ecosystems necessitates the development of sustainable biodegradation strategies. This study aimed to evaluate the LDPE-degrading potential of the gut bacterial strain P. megaterium RP1/S1 and to formulate a shelf-stable liquid bioinoculant for field-level plastic biodegradation. The bacterium exhibited strong polymer-degrading enzymatic activity when LDPE was the sole carbon source, with laccase increasing from 0.98 ± 0.03-1.97 ± 0.05 U/mL, manganese peroxidase from 1.42 ± 0.04-2.09 ± 0.06 U/mL, esterase from 5.85 ± 0.15-1.98 ± 0.05 U/mL, and lipase from 0.73 ± 0.02-2.46 ± 0.07 U/mL over 30 days compared to the control. Liquid bioinoculant formulation trials revealed that Trehalose 10 mM was the best stabiliser, sustaining 10.23 × 10⁹ CFU/mL after 360 days, outperforming PEG, PVP, glycerol, Tween-80, and Polysorbate-20. Biodegradation of LDPE films in soil across six treatments showed that the integrated amendment treatment (APT6: P. megaterium RP1/S1 + cow dung + vegetable waste + cocopeat) was the most effective. APT6 recorded the highest microbial proliferation (203 ± 7.32 CFU/mL at 90 days) with colour (dark yellow), odour (less), pH (6.9) and turbidity (higher), maximum micronutrient enhancement (Fe 12.27 µg g⁻¹, Zn 4.30 µg g⁻¹, Mn 27.45 µg g⁻¹, Cu 2.85 µg g⁻¹) and the greatest improvement in soil carbon fractions (soil organic carbon (1.12%), soil inorganic carbon (3.50%), total carbon (4.63%) labile carbon (246.12 mg/kg), mineralizable carbon (495.98 mg/kg), microbial biomass carbon (47.21 mg/kg) compared to control. FT-IR revealed the disappearance of O-H groups and formation of new CO and C-O peaks, surface deterioration confirmed through AFM, while SEM-EDS confirmed severe surface pitting and a reduction of elemental carbon from 95.24% to 54.84% (mass) with a concomitant oxygen increase to 19.21% (mass). LDPE degradation indicators were strongest in APT6, where crystallinity decreased from 71.38% to 68.40%, weight loss increased to 41.73%, GSM decreased from 64.3 ± 1.70-42.5 ± 1.53 g/m², and tensile strength declined from 9.93 to 7.32 MPa compared to control (APT1), indicating significant structural deterioration of LDPE. These findings indicate that the application of stabilized bioformulations of P. megaterium RP1/S1 in conjunction with organic amendments substantially promotes the partial biodegradation, oxidative depolymerization, and structural deterioration of LDPE in soil environments, potentially reducing plastic accumulation in ecosystems and contributing to sustainable waste remediation practices.