Marine bacterial biodegradation of low-density polyethylene (LDPE) plastic

Polyethylene has considered as non-degradable for decades, and their degradation through marine bacteria has rarely studied. However, LDPE found a significant source of pollution in the marine environment. In the present study, four bacterial strains capable of biodegradation of LDPE were isolated from the marine environment. These bacterial isolates H-237, H-255, H-256 and H-265 were revealed close similarity with Cobetia sp., Halomonas sp., Exigobacterium sp. and Alcanivorax sp., respectively based on 16S rRNA gene sequencing method. These bacterial isolates were individually incubated for 90 days supplied with LDPE films as a carbon source using the Bushnell-Haas medium. During the biodegradation assay, bacterial isolates were formed the viable biofilm on the LDPE surface, which decreased the thermal stability of the films. At the end of the incubation study, a maximum weight loss of 1.72% of LDPE film was observed by the bacterial isolate H-255. The bacterial attachment on the film changed the physical structure (surface erosion, roughness and degradation) which were confirmed by field emission scanning electron microscopy and atomic force microscopy. The changes in the chemical structure of the LDPE film were analyzed by Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). This ATR-FTIR showed the shifting of peaks of C-H stretch and C=C bond stretching and the new peaks formation of C-O and -C=C- bonds in comparison to control LDPE film. Further, biodegradation of LDPE film was also confirmed by remineralization of carbon and enzymatic activities. This study revealed that the active biodegradation of LDPE film by marine bacteria and these bacteria could reduce plastic pollution in the marine environment.