Characterization of a low-density polyethylene-oxidizing enzyme in Pseudomonas aeruginosa via transcriptomic and proteomic analysis

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 CO 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.