Biodegradation of polyethylene film by the Bacillus sp. PELW2042 from the guts of Tenebrio molitor (Mealworm Larvae)

Abstract

The chemical molecular structure of polyethylene (PE) is very stable and extremely difficult to degrade in the environment, thus posing a threat to the environment. In this study, a high-density polyethylene (HDPE)-degrading Bacillus strain PELW2042, was isolated from the gut contents of Tenebrio molitor larvae (yellow mealworms). Results showed that after 42 days of incubation with PELW2042, a large number of pits and cracks were observed on the surface of HDPE film by scanning electron microscopy (SEM). The Fourier Transform-Infrared Spectroscopy (FT-IR) detected absorption peaks near 1700 cm-1 and 1249 cm-1, indicating the formation of carbonyl groups (–CO) and ether groups (–C–O); the X-ray photoelectron spectroscopy (XPS) spectra further demonstrated the generation of new oxygen-containing functional groups. X-Ray Diffraction (XRD) and differential scanning calorimetry (DSC) analyses revealed a 21.63 ± 0.18 % decrease in the relative crystallinity of the HDPE film, indicating that the structure of the HDPE changes. Finally, it was also shown that the weight loss of HDPE film was as high as 17.36 ± 0.56 %. After 42 days of treatment by strain PELW 2042, the molecular weights of the experimental group samples were significantly decreased by 23.31 ± 1.25 % and 30.07 ± 1.37 % for Mw (121700 Da) and Mn (50700 Da), respectively, compared to those of the untreated samples (Mw=158700 Da and Mn=72500 Da). All these results indicate that Bacillus sp. PELW2042 has a high ability to degrade HDPE. This provides a source of strains to accelerate the biodegradation of waste polyethylene plastics.