wcm.02.2026.303.308

Understanding how local bacterial communities interact with different plastic types in freshwater ecocystems remains limited, despite the continuous accumulation of synthetic polymers. The objective of this study was to use a raw microbial community from the Tigris River as a natural inoculum to evaluate its biodegradation potential. As the sole carbon sources, High-density polyethylene (HDPE) and polyethene terephthalate (PET) were subjected to 90 days of controlled laboratory conditions. Analysis of colony-forming units (CFU/ml) revealed significant differences in colonization dynamics (p <= 0.001) . HDPE showed irregular semistable growth, while PET supported continuous bacterial increase. 16S rRNA sequencing showed a consortium dominated by Pseudomonas aeruginosa (GJ-TIG1), Bacillus subtilis (GJ-TIG2), and Bacillus subtilis (GJ-TIG3), suggesting functional cooperation. The GJ-TIG1 strain likely acts as the first colonizer by oxidizing the plastic surface, which enables GJ-TIG2 and GJ-TIG3 to use enzymatic hydrolysis of ester bonds. These biological findings were confirmed by physical and chemical analyses. Field-emission scanning electron microscopy (FESEM) showed distinct damage in PET compared with limited surface changes in HDPE. Fourier transform infrared (FTIR) and gas chromatography-mass spectrometry (GC-MS) analyses supported this difference by detecting breaking of the ester bonds and the formation of by-products such as phthalates and hydrocarbons. These results indicate partial biodegradation by a natural consortium, with its effectiveness deppending on the type of polymer. This study therefore provides basic insights into bioremediation of microplastic contamination in the Tigris River, which often suffer from a scarcity of such studies.