Abstract
Background:
Plastic pollution, particularly microplastics, represents a persistent environmental threat due to their accumulation and ecological hazards. Biodegradation using bacteria provides a sustainable and ecofriendly strategy for mitigating plastic waste.

Aim:
This study aimed to evaluate the biodegradation potential of B. cereus and B. subtilis against high-density polyethylene (HDPE) microplastics.

Methods:
A 9 × 9-cm HDPE film was inoculated with either bacterial strain in 100 mL Bushnell-Haas (BH) medium for 90 days. Biodegradation was assessed by povidone-iodine dye permeability, scanning electron microscopy, Fourier-transform infrared spectroscopy, weight loss measurement, light scattering, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis.

Results:
The dye test revealed increased permeability, suggesting pore formation. SEM confirmed structural modifications, with average pore diameters of 150.08 and 100.21 nm in B. cereus and 100.21 nm in B. subtilis. FT-IR indicated new functional groups and bond modifications, consistent with polymer chain breakdown. Weight loss analysis after 30 days showed reductions of 2.2% and 3.8% for B. cereus and B. subtilis, respectively. Light scattering demonstrated decreased plastic fragment size. SDS-PAGE revealed the presence of extracellular proteins, including a ~100 kDa band in B. subtilis, implying enzymatic involvement in the degradation process.

Conclusion:
Both B. cereus and B. subtilis degraded HDPE microplastics, with B. subtilis showing slightly higher efficiency. These findings support their potential as bioremediation agents for plastic-contaminated environments.

Key words: Bacillus cereus; Bacillus subtilis; Biodegradation; High-density polyethylene (HDPE); SDS-PAGE.