Biodegradation of polyethylene and polystyrene by Zophobas atratus larvae from Bangladeshi source and isolation of two plastic-degrading gut bacteria.

Plastic pollution has become a major environmental concern globally, and novel and eco-friendly approaches like bioremediation are essential to mitigate the impact. Low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and expanded polystyrene (EPS) are three of the most frequently used plastic types. This study examined biodegradation of these using Zophobas atratus larvae, followed by isolation and whole genome sequencing of gut bacteria collected from larvae frass. Over 36 days, 24.04 % LDPE, 20.01 % EPS, and 15.12 % LLDPE were consumed on average by the larvae, with survival rates of 85 %, 90 %, and 87 %, respectively. Fourier transform infrared spectroscopy (FTIR) analysis of fresh plastic types, consumed plastics, and larvae frass showed proof of plastic oxidation in the gut. Frass bacteria were isolated and cultured in minimal salt media supplemented with plastics as the sole carbon source. Two isolates of bacteria were sampled from these cultures, designated PDB-1 and PDB-2. PDB-1 could survive on LDPE and LLDPE as carbon sources, whereas PDB-2 could survive on EPS. Scanning Electron Microscopy (SEM) provided proof of degradation in both cases. Both isolates were identified as strains of Pseudomonas aeruginosa, followed by sequencing, assembly, and annotation of their genomes. LDPE- and LLDPE-degrading enzymes e.g., P450 monooxygenase, alkane monooxygenase, alcohol dehydrogenase, etc. were identified in PDB-1. Similarly, phenylacetaldehyde dehydrogenase and other enzymes involved in EPS degradation were identified in PDB-2. Genes of both isolates were compared with genomes of known plastic-degrading P. aeruginosa strains. Virulence factors, antibiotic-resistance genes, and rhamnolipid biosurfactant biosynthesis genes were also identified in both isolates. This study indicated Zophobas atratus larvae as potential LDPE, LLDPE, and EPS biodegradation agent. Additionally, the isolated strains of Pseudomonas aeruginosa provide a more direct and eco-friendly solution for plastic degradation. Confirmation and modification of the plastic-degrading pathways in the bacteria may create scope for metabolic engineering in the future.

Zaman I ，Turjya RR ，Shakil MS ，Al Shahariar M ，Emu MRRH ，Ahmed A ，Hossain MM ... -  《-》

Biodegradation of low-density polyethylene and polystyrene in superworms, larvae of Zophobas atratus (Coleoptera: Tenebrionidae): Broad and limited extent depolymerization.

Larvae of Zophobas atratus (synonym as Z. morio, or Z. rugipes Kirsch, Coleoptera: Tenebrionidae) are capable of eating foams of expanded polystyrene (EPS) and low-density polyethylene (LDPE), similar to larvae of Tenebrio molitor. We evaluated biodegradation of EPS and LDPE in the larvae from Guangzhou, China (strain G) and Marion, Illinois, U.S. (strain M) at 25 °C. Within 33 days, strain G larvae ingested respective LDPE and PS foams as their sole diet with respective consumption rates of 58.7 ± 1.8 mg and 61.5 ± 1.6 mg 100 larvae-1d-1. Meanwhile, strain M required co-diet (bran or cabbage) with respective consumption rates of 57.1 ± 2.5 mg and 30.3 ± 7.7 mg 100 larvae-1 d-1. Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and thermal gravimetric analyses indicated oxidation and biodegradation of LDPE and EPS in the two strains. Gel permeation chromatography analysis revealed that strain G performed broad depolymerization of EPS, i.e., both weight-average molecular weight (Mw) and number-average molecular weight (Mn) of residual polymers decreased, while strain M performed limited extent depolymerization, i.e., Mw and Mn increased. However, both strains performed limited extent depolymerization of LDPE. After feeding antibiotic gentamicin, gut microbes were suppressed, and Mw and Mn of residual LDPE and EPS in frass were basically unchanged, implying a dependence on gut microbes for depolymerization/biodegradation. Our discoveries indicate that gut microbe-dependent LDPE and EPS biodegradation is present within Z. atratus in Tenebrionidae, but that the limited extent depolymerization pattern resulted in undigested polymers with high molecular weights in egested frass.

Peng BY ，Li Y ，Fan R ，Chen Z ，Chen J ，Brandon AM ，Criddle CS ，Zhang Y ，Wu WM ... -  《-》

Biodegradation of expanded polystyrene and low-density polyethylene foams in larvae of Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae): Broad versus limited extent depolymerization and microbe-dependence versus independence.

Yellow mealworms (Tenebrio molitor larvae) are capable of biodegrading polystyrene (PS) and low-density polyethylene (LDPE). This study tested biodegradation of one expanded PS (EPS) with a weight-average molecular weight (Mw) 256.4 kDa and two LDPE foams with respective Mw of 130.6 kDa (PE-1) and 288.7 kDa (PE-2) in T. monitor larvae obtained in Beijing, China. The larvae consumed EPS and both LDPEs over a 60 day. Fourier transform infrared spectroscopy and thermogravimetric analyses of frass confirmed the formation of new oxygen-containing functional groups, as well as a change in physical property and chemical modification, indicating that biodegradation of EPS and LDPE occurred. Gel permeation chromatography analysis confirmed broad depolymerization of EPS and PE-1 (i.e., a decrease in both Mw and a number-average molecular weight (Mn)) but revealed limited extent depolymerization of PE-2 (i.e., increase in Mn and decrease in Mw). For all materials, the size-average molecular weight (Mz) was decreased. Biodegradation and oxidation of EPS and LDPE were confirmed using FTIR and TGA analysis. Depression of gut microbes by the antibiotic gentamicin resulted in significant inhibition of EPS depolymerization but did not stop LDPE depolymerization, resulting in the increase in Mn and revealing that PS biodegradation was gut microbe-dependent but LDPE biodegradation was less dependent or independent of gut microbes. Gut microbial community analysis indicated that, as expected, under different dietary conditions, the intestinal flora significantly shifted to communities associated with biodegradation of EPS and LDPE. The results indicated the complexity and limitation of biodegradation of plastics in plastics-eating T. molitor larvae.

Yang L ，Gao J ，Liu Y ，Zhuang G ，Peng X ，Wu WM ，Zhuang X ... -  《-》

Biodegradation of foam plastics by Zophobas atratus larvae (Coleoptera: Tenebrionidae) associated with changes of gut digestive enzymes activities and microbiome.

In order to uncover the plastic types that superworm Zophobas atratus can degrade and the underlying changes associated with plastics consumption, three types of plastics including polystyrene (PS), polyethylene (PE) and polyurethane (PU) foam were used as sole feedstock to feed the superworm larvae for 35 days with bran as control. Compared to the control, PS- or PU-fed larvae showed 100% survival rates, the PE-fed and starvation larvae had decreased survival rates of 81.67% and 65%, respectively. Both plastics-fed and starvation groups showed decreased larvae weight. The consumption rates of PS, PE, and PU were 1.41, 0.30, and 0.74 mg/d/larva, respectively. The attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and differential scanning calorimeter and thermogravimetric (DSC-TGA) analyses demonstrated the changes of functional groups and thermostability in frass compared to plastic feedstocks, indicating the partial oxidation and degradation of plastics. Among the gut digestive enzymes tested, protease showed increased activities in all plastics-fed groups. Gut microbial communities displayed significant relative abundance changes such as increased abundances of Enterococcus in all plastic-fed groups, Citrobacter in PE-fed group, Dysgonomonas and Sphingobacterium in PS-fed group, and Mangrovibacter in PU-fed group. The latter 3 genera were reported for the first time. In summary, the results demonstrated that Z. atratus could efficiently degrade both PS and PU foam plastics, and the plastic degradation was associated with changes of gut microbial communities and digestive enzyme activities.

Luo L ，Wang Y ，Guo H ，Yang Y ，Qi N ，Zhao X ，Gao S ，Zhou A ... -  《-》

Biodegradation of polystyrene by three bacterial strains isolated from the gut of Superworms (Zophobas atratus larvae).

To isolate polystyrene-degrading bacteria from the gut of superworms and investigate their ability to degrade polystyrene (PS). Three PS-degrading bacteria identified as Pseudomonas sp. EDB1, Bacillus sp. EDA4 and Brevibacterium sp. EDX were successfully isolated from the gut of superworms (Zophobas atratus Larvae) that ingest PS. Incubating PS with each strain for 30-day led to the formation of biofilm on the PS film. Scanning electron microscopy (SEM) revealed considerable damage (in terms of pits formation) on the surface of the PS films. FTIR analysis suggested the incorporation of carbonyl group into the carbon backbone of PS. Decreasing of WCA of microbial-treated PS film confirmed a chemical change from hydrophobicity to hydrophilicity on the PS surface. Based on these results, we conclude that all isolates had the ability to degrade PS. Brevibacterium sp. EDX (GenBank MZ32399) was isolated as the most efficient PS-degrading strain based on the most changing in both PS surface morphology (SEM and WCA analyses) and chemical modification (FTIR analysis) in its PS degradation process. This was the first study to describe the PS degradation by Brevibacterium sp. EDX, and thus provided for its development in the plastic remediation process.

Arunrattiyakorn P ，Ponprateep S ，Kaennonsang N ，Charapok Y ，Punphuet Y ，Krajangsang S ，Tangteerawatana P ，Limtrakul A ... -  《-》