Investigation of Polyethylene (PE) Exposure in Labeo rohita (Hamilton, 1822): Accumulation, Stress Responses and In Vitro Biodegradation of PE by a Gut-Associated Bacterium.

The aquatic biome is exposed to a significant threat of persistent contamination by polyethylene (PE) in the ecosystem. A critical research gap exists in PE-induced tissue-specific bioaccumulation, associated immune and stress responses in fish, followed by potential bioremediation solutions. The present study investigated the bioaccumulation of PE particles and subsequent oxidative stress in Labeo rohita induced by two different doses (0.1 and 0.5 mg/L) over 2 weeks. Additionally, the biodegradation potential of gut-associated microbial isolates was also evaluated. We found that PE accumulation was highest in the intestine (33.0 ± 2.5 particles/g), followed by gills (20.5 ± 1.9 particles/g) and liver (8.0 ± 1.4 particles/g), indicating a significant, dose- and time-dependent increase. Substantially, it triggered a tissue-wise oxidative stress response of antioxidant (SOD, CAT, GPx) and stress marker (Hsp70) genes, showing significant upregulation in gill, liver, and intestine. Furthermore, this work identified a gut-associated bacterium, Proteus vulgaris KG-SD-15807, demonstrating significant PE biodegradation capability. Quantitative analysis revealed achievement of 3.00% ± 0.16% weight loss over 30 days of incubation. Qualitative characterization through FT-IR, FE-SEM, and GC-MS analyses indicated polymer oxidation, surface erosion, and formation of distinct metabolic degradation intermediates. The present findings reveal the significant bioaccumulation and stress response due to PE in a commercially important fish, Labeo rohita. Moreover, the identified bacterium acted as a PE biodegradation agent. This research has significant implications for future explorations focused on the long-term impacts of PE in aquatic animals and the optimization of biodegradation efficiency of Proteus vulgaris for applied bioremediation.