| Due to the characteristics of high strength,flexibility,wear resistance,light weight,easy production and low processing cost,plastics have been widely used in various fields,promoting the advancement of modern human society.However,most plastics are discarded after single use,and a large number of plastic wastes are buried,burned or even directly exposed to the land and marine environment due to lack of appropriate managements,posing serious threats to the ecological environment and human health.In recent years,the biodegradation of plastics has become a hotspot.Enzymatic degradation of polyethylene terephthalate(PET)has been studied from multiple angles,including enzymology,catalytic mechanism,and enzyme engineering,making PET enzymatic degradation potentially applicable.However,the degradation of polyolefin plastics is much more difficult than that of polyester plastics,and the resources of polyolefin-degrading strains and enzymes are still scarce,and the degradation mechanism is still unclear.Therefore,it is of great significance to isolate polyolefin-degrading strains and uncover their related enzymes,which will benefit the elucidation of polyolefin degradation pathways and mechanisms.The main focus of this study is to screen and isolate polyolefin-degrading strains from the gut of mealworms,and to perform whole-genome sequencing and data mining for the polyolefindegrading enzymes.First,polystyrene foam was fed to yellow mealworm larvae to enrich bacteria strains capable of degrading polystyrene.The intestinal suspension was then cultured using polystyrene as the sole carbon source to obtain strains that potentially degrade polystyrene.The degradation capacity was subsequently verified on agar plates.A bacterial strain Enterobacter sp.strain EET0601 was then identified as a polystyrene degrader.For the characterization of the degradation ability,the strain was cultured with polyethylene or polystyrene film as the sole carbon source on minimal medium plate.Scanning electron microscopy showed obvious erosion on the surface of the film,and water contact angle detection showed reduced hydrophobicity of the film.Appearance of new functional groups was determined by Fourier transform infrared spectrometer.The-OH and C-O groups were detected on the surface of the PS film,whereas the-OH,C=C and C-O groups were detected on the surface of PE film.Collectively,these results indicated that strain EET0601 could degrade PS and PE films.For the identification of enzymes responsible for polystyrene and polyethylene degradation,the whole genome of the strain was sequenced.The obtained draft genome has a size of 4.7 Mbp with a GC content of 54.8 mol%,consisting of 21 scaffolds and 4,454 genes.To date,all reported polyolefin-degrading enzymes are peroxidases.Coincidently,a dyedecolorizing peroxidase(EhDyP)in this strain meets an important feature—capable of catalyzing oxidation reactions on the enzyme surface through long-range electron transfer.Subsequently,the enzyme was heterologously expressed and purified.The function of the enzyme was characterized by incubation with polystyrene and polyethylene films.The obvious erosion of the film surface was observed by scanning electron microscopy;the increase of the surface roughness was observed by atomic force microscope;the reduced hydrophobicity of the film was determined by water contact angle detection;and new functional groups(-OH and C=C)on the film surface was detected by Fourier transform infrared spectrometer.These results indicate that the EhDyP found in the EET0601 can degrade polystyrene and polyethylene films.In summary,this study isolated a bacterial strain,Enterobacter sp.strain EET0601,from the gut of mealworms.This strain can degrade polystyrene and polyethylene.Moreover,a dyedecolorizing peroxidase,EhDyP,was identified to be capable of degrading polystyrene and polyethylene.This study has enriched the resources for biodegradation of polystyrene and polyethylene and is of great significance for solving plastic pollution. |
