Recently, various attempts have been made to solve plastic waste problems, such as development of biodegradation without producing pollution. Polystyrene (PS) is the fifth most used plastic in many industries; therefore, degrading PS becomes a critical global issue. Here, we reported Pseudomonas aeruginosa strain DSM 50071, initially isolated from the gut of the superworms, Zophobas atratus, and the PS degradation by Pseudomonas sp. DSM 50071. We examined PS degradation using electronic microscopy and measured changes in atomic composition and contact angles with water droplets on the PS surface that represents a chemical change from hydrophobicity to hydrophilicity. We have further examined chemical structural changes using X-ray photoelectron spectroscopy, Fourier-transform-infrared spectroscopy, and nuclear magnetic resonance (NMR) to confirm the formation of carbonyl groups (CO) in the oxidation pathway during PS biodegradation. In reverse transcription quantitative polymerase chain reaction analysis, the gene expression level of serine hydrolase (SH) in Pseudomonas sp. DSM 50071 was highly increased during PS degradation, and the enzyme-mediated biodegradation of PS was further confirmed by the SH inhibitor treatment test. Thus, the significance of these findings goes beyond the discovery of a novel function of Pseudomonas sp. DSM 50071 in the gut of superworms, highlighting a potential solution for PS biodegradation.

Plastic waste worldwide is becoming a serious pollution problem for the planet. Various physical and chemical methods have been tested in attempts to remove plastic dumps. However, these have usually resulted in secondary pollution issues. Recently, the biodegradation of plastic by fungal and bacterial strains has been spotlighted as a promising solution to remove plastic wastes without generating secondary pollution. We have previously reported that a Pseudomonas aeruginosa strain isolated from the gut of a superworm is capable of biodegrading polystyrene (PS) and polyphenylene sulfide (PPS). Herein, we demonstrate the extraordinary biodegradative power of P. aeruginosa in efficiently depolymerizing four different types of plastics: PS, PPS, polyethylene (PE) and polypropylene (PP). We further compared biodegradation rates for these four plastic types and found that PE was biodegraded fastest, whereas the biodegradation of PP was the slowest. Moreover, the growth rates of P. aeruginosa were not always proportional to biodegradation rates, suggesting that the rate of bacterial growth could be influenced by the composition and properties of intermediate molecules produced during plastic biodegradation, and these may supply useful cellular precursors and energy. In conclusion, an initial screening system to select the most suitable bacterial strain to biodegrade certain types of plastic is particularly important and may be necessary to solve plastic waste problems both presently and in the future.

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<p>Large quantities of plastic waste represent a grave social issue. Various attempts have been made to solve plastic waste problems, such as methods of natural plastic degradation. Currently, polystyrene (PS) is one of the most widely used plastics in many industries; therefore, degrading PS becomes a critical global issue. In this study, we isolated <i>Pseudomonas</i> sp., a strain of plastic-degrading bacteria known to survive only in the soil, from the gut of the superworms. Thus far, the degradation of PS by <i>Pseudomonas</i> sp. has barely been explored. We examined PS degradation using electronic microscopy, and measured changes in atomic distribution and contact angles with water droplets on the PS surface that represent a chemical change from hydrophobicity to hydrophilicity. During the process of PS degradation by <i>Pseudomonas</i> sp., we examined chemical structural changes using X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR) to check for the formation of C=O bonds and changes towards hydrophilicity. RT-qPCR was used to measure the gene expression level of <a></a><a>serine hydrolase </a>in <i>Pseudomonas</i>, an enzyme that mediates the plastic degradation. Our findings indicate that <i>Pseudomonas</i> present in the gut of the superworms participates in the degradation of plastics following ingestion. Moreover, this study also identified a candidate enzyme related to PS degradation in <i>Pseudomonas</i> for the first time. Thus, the findings of this study prove significance not only in presenting a novel function of <i>Pseudomonas</i> in the gut of superworms, but also in highlighting a potential solution for PS degradation.<b></b></p>