https://scholar.dgist.ac.kr/handle/20.500.11750/11713 2026-04-04T16:56:57Z https://scholar.dgist.ac.kr/handle/20.500.11750/58390 Title: Characterization of a low-density polyethylene-oxidizing enzyme in Pseudomonas aeruginosa via transcriptomic and proteomic analysis Author(s): Kim, Hong Rae; Lee, Ye Eun; Lee, Eunkyo; Suh, Dong-Eun; Choi, Donggeun; Lee, Sukkyoo Abstract: Plastics have become indispensable in modern industries; however, their resistance to natural degradation poses environmental challenges. Biological degradation technologies employing microorganisms offer promising solutions. Here, we analyzed the transcriptome and proteome of Pseudomonas aeruginosa, a plastic-degrading microorganism found in the gut of superworms, to identify the genes and enzymes upregulated during low-density polyethylene (LDPE) degradation. Functional analyses of these upregulated genes and enzymes using the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology databases revealed an increase in lipid and hydrophobic amino acid metabolism, suggesting their involvement in LDPE degradation. Based on these analyses, we identified phenylalanine monooxygenase (PAH), which is capable of oxidizing plastics. To investigate the involvement of the enzyme in LDPE degradation, phhA was transformed into Escherichia coli, and the enzymes were produced and purified. The purified enzymes were then reacted with LDPE and analyzed. The results revealed the formation of hydroxyl (-OH) and C[sbnd]O groups on the LDPE surface after treatment with PAH, confirming its ability to oxidize LDPE. LDPE is highly hydrophobic and exhibits extremely low reactivity, making it resistant to degradation. The PAH introduces oxygen-containing functional groups into LDPE, increasing its reactivity and thereby facilitating its biodegradation. In this study, we discovered an enzyme capable of catalyzing the oxidation step (the initial stage of LDPE biodegradation) and experimentally validated its activity. © 2025 2025-04-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/57367 Title: Enhancing the oxidation of polystyrene through a homogeneous liquid degradation system for effective microbial degradation Author(s): Kim, Hong Rae; Koh, Hye Yeon; Shin, Hyeyoung; Suh, Dong-Eun; Lee, Sukkyoo; Choi, Donggeon Abstract: Plastics play a crucial role in modern industries; however, their resistance to natural degradation contributes to environmental pollution, and microplastics pose a health threat. The hydrophobic nature of microplastics poses a considerable challenge, rendering them resistant to dissolving in water. In this study, we conducted a comparative analysis of the microbial biodegradation capabilities of polystyrene in solid and liquid states. Polystyrene in its solid foam form, along with polystyrene converted into a liquid state using ethyl-ester oil, was biodegraded by microorganisms. Subsequently, the liquid plastic was re-extracted into its solid form, and the degree of degradation was assessed using weight loss measurement, XPS, FT-IR, GPC, and TGA. Liquid-state polystyrene exhibited a higher degradation rate than that reported previously. Furthermore, liquid polystyrene undergoes more pronounced oxidation than its solid counterpart, leading to an increased oxygen atom ratio. Chemical structure analysis highlighted the distinct formation of –OH and C=O functional groups in the liquid state compared to those in the solid state. Additionally, notable changes in the molecular weight and thermal stability of polystyrene were observed during biodegradation in the liquid state. This study suggests that a heterogeneous reaction (solid plastic-liquid medium) might impede plastic biodegradation, while indicating the potential to enhance the degradation efficiency through a homogeneous reaction (liquid plastic-liquid medium). The follow-up study identifies appropriate solvents and optimizes cultivation conditions, offering potential to enhance the efficiency of biological plastic degradation. Copyright © 2024 Kim, Koh, Shin, Suh, Lee and Choi. 2024-10-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/57187 Title: Biodegradation of Ethylene Vinyl Acetate Using Klebsiella aerogenes EM011 Isolated from Effective Microorganisms Author(s): Maidarjav, Amarbayasgalan; Nyamjav, Indra; Kim, Hong Rae; Suh, Dong-Eun; Lee, Sukkyoo Abstract: The amount of global plastic waste on land or in marine environments is a critical environmental issue. Plastic biodegradation by microorganisms, insect larvae, and enzymes has become one of the most popular solutions due to the ability of this strategy to generate environmentally benign byproducts, addressing ecological plastic waste concerns. This study revealed the biodegradation of ethylene vinyl acetate (EVA) by the bacterial strain identified as Klebsiella aerogenes EM011, isolated from effective microorganisms. The study found that K. aerogenes EM011 can survive in a carbon-free medium for 30 days using EVA films as the sole energy source, decomposing 0.65 ± 0.04% of 1g of EVA film. The surface changes of the film were detected using scanning electron microscopy after treatment with K. aerogenes EM011. In addition, elemental modifications were detected in the imaged area of the plastic surfaces by energy-dispersive X-ray spectroscopy. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses were conducted to detect changes in the functional groups and chemical components, elucidating alterations on the surface of the EVA films. Through these physicochemical analyses, the formation of carbonyl groups (C=O), ester groups (C–O), and hydroxyl groups (–OH) confirmed the oxidation of EVA. Furthermore, the oxidation led to the decomposition of the EVA film, resulting in changes in its thermal stability and molecular weight distribution. These findings show that the K. aerogenes EM011 strain plays a role in accelerating the biodegradation of EVA. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024. 2024-10-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/57050 Title: Identification of plastic-degrading bacteria in the human gut Author(s): Jang, Yejin; Nyamjav, Indra; Kim, Hong Rae; Suh, Dong-Eun; Park, Nohyoon; Lee, Ye Eun; Lee, Sukkyoo Abstract: Environmental pollution caused by the excessive use of plastics has resulted in the inflow of microplastics into the human body. However, the effects of microplastics on the human gut microbiota still need to be better understood. To determine whether plastic-degrading bacteria exist in the human gut, we collected the feces of six human individuals, did enrichment cultures and screened for bacterial species with a low-density polyethylene (LDPE) or polypropylene (PP)-degrading activity using a micro-spray method. We successfully isolated four bacterial species with an LDPE-degrading activity and three with a PP-degrading activity. Notably, all bacterial species identified with an LDPE or PP-degrading activity were opportunistic pathogens. We analyzed the microbial degradation of the LDPE or PP surface using scanning electron microscopy and confirmed that each bacterial species caused the physical changes. Chemical structural changes were further investigated using X-ray photoelectron spectroscopy and Fourier-transform-infrared spectroscopy, confirming the oxidation of the LDPE or PP surface with the formation of carbonyl groups (C=O), ester groups (C[sbnd]O), and hydroxyl groups (-OH) by each bacterial species. Finally, high temperature gel permeation chromatography (HT-GPC) analysis showed that these bacterial species performed to a limited extent depolymerization. These results indicate that, as a single species, these opportunistic pathogens in the human gut have a complete set of enzymes and other components required to initiate the oxidation of the carbon chains of LDPE or PP and to degrade them. Furthermore, these findings suggest that these bacterial species can potentially biodegrade and metabolize microplastics in the human gut. © 2024 Elsevier B.V. 2024-05-31T15:00:00Z