Potential of esterase DmtH in transforming plastic additive dimethyl terephthalate to less toxic mono-methyl terephthalate

How micro-/nano-plastics influence the horizontal transfer of antibiotic resistance genes - A review

Plastic debris such as microplastics (MPs) and nanoplastics (NPTs), along with antibiotic resistance genes (ARGs), are pervasive in the environment and are recognized as significant global health and ecological concerns. Micro-/nano-plastics (MNPs) have been demonstrated to favor the spread of ARGs by enhancing the frequency of horizontal gene transfer (HGT) through various pathways. This paper comprehensively and systematically reviews the current study with focus on the influence of plastics on the HGT of ARGs. The critical role of MNPs in the HGT of ARGs has been well illustrated in sewage sludge, livestock farms, constructed wetlands and landfill leachate. A summary of the performed HGT assay and the underlying mechanism of plastic-mediated transfer of ARGs is presented in the paper. MNPs could facilitate or inhibit HGT of ARGs, and their effects depend on the type, size, and concentration. This review provides a comprehensive insight into the effects of MNPs on the HGT of ARGs, and offers suggestions for further study. Further research should attempt to develop a standard HGT assay and focus on investigating the impact of different plastics, including the oligomers they released, under real environmental conditions on the HGT of ARGs.

Co-upcycling of Plastic Waste and Biowaste via Tandem Transesterification Reactions

Polyethylene terephthalate (PET) and glycerol are prevalent forms of plastic and biowaste, necessitating facile and effective strategies for their upcycling treatment. Herein, we present an innovative one-pot reaction system for the concurrent depolymerization of PET plastics and the transesterification of glycerol into dimethyl terephthalate (DMT), a valuable feedstock in polymer manufacturing. This process occurs in the presence of methyl acetate (MA), a byproduct of the industrial production of acetic acid. The upcycling of biowaste glycerol into glycerol acetates renders them valuable additives for application in both the biofuel and chemical industries. This integrated reaction system enhances the conversion of glycerol to acetins compared with the singular transesterification of glycerol. In this approach, cost-effective catalysts, based on perovskite-structured CaMnO3, were employed. The catalyst undergoes in situ reconstruction in the tandem PET/glycerol/MA system due to glycerolation between the metal oxides and glycerol/acetins. This process results in the formation of small metal oxide nanoparticles confined in amorphous metal glycerolates, thereby enhancing the PET depolymerization efficiency. The optimized coupled reaction system can achieve a product yield exceeding 70% for glycerol acetates and 68% for PET monomers. This research introduces a tandem pathway for the simultaneous upcycling of PET plastic waste and biowaste glycerol with minimal feedstock input and maximal reactant utilization efficiency, promising both economic advantages and positive environmental impacts.

Review of nomenclature and methods of analysis of polyethylene terephthalic acid hydrolyzing enzymes activity

Enzymatic degradation of polyethylene terephthalic acid (PET) has been gaining increasing importance. This has resulted in a significant increase in the search for newer enzymes and the development of more efficient enzyme-based systems. Due to the lack of a standard screening process, screening new enzymes has relied on other assays to determine the presence of esterase activity. This, in turn, has led to various nomenclatures and methods used to describe them and measure their activity. Since all PET-hydrolyzing enzymes are α/β hydrolases, they catalyze a serine nucleophilic attack and cleave an ester bond. They are lipases, esterases, cutinases and hydrolases. This has been used interchangeably, leading to difficulties while comparing results and evaluating progress. This review discusses the varied enzyme nomenclature being adapted, the different assays and analysis methods reported, and the strategies used to increase PET-hydrolyzing enzyme efficiency. A section on the various ways to quantify PET hydrolysis is also covered.

Long-term exposure to polystyrene nanoparticles at environmentally relevant concentration causes suppression in heme homeostasis signal associated with transgenerational toxicity induction in Caenorhabditis elegans

Heme homeostasis related signaling participates in inducing a protective response when controlling nanopolystyrene toxic effects in parental generation. However, whether the heme homeostasis signal is involved in regulation of transgenerational toxicity of nanopolystyrene toxicity is still unclear. Herein, with the model organism of Caenorhabditis elegans, 0.1-10 μg/L nanopolystyrene particles (PS-NPs) at 20-nm treatment downregulated glb-18, and the decrease was also discovered in the offspring following PS-NPs exposure. Germline glb-18 RNAi induced susceptive property to transgenerational PS-NPs toxicity, suggesting that a decreased GLB-18 level mediated induction of transgenerational toxicity. Importantly, germline GLB-18 transgenerationally activated the function of intestinal HRG-4 in controlling transgenerational PS-NPs toxicity. In transgenerational toxicity control, HRG-1/ATFS-1/HSP-6 was recognized to be the downstream pathway of HRG-4. Briefly, germline GLB-18 in P0 generation can transgenerationally activate the downstream intestinal HRG-4/HRG-1/ATFS-1/HSP-6 pathway among offspring for controlling the transgenerational toxicity of PS-NPs. Findings in the present work strengthens the possible association of heme homeostasis signal changes with transgenerational nanoplastic toxicity within the organisms.

Microplastics Enhance the Prevalence of Antibiotic Resistance Genes in Anaerobic Sludge Digestion by Enriching Antibiotic-Resistant Bacteria in Surface Biofilm and Facilitating the Vertical and Horizontal Gene Transfer

Antibiotic resistance genes (ARGs) and microplastics (MPs) are recognized as emerging contaminants and threats to global human health. Despite both of them being significantly detected in their "hotspots", i.e., waste activated sludge (WAS), rare studies on how MPs affect ARGs and antibiotic-resistant bacteria (ARB) in anaerobic sludge digestion are available. Herein, the fate of ARGs and ARB after exposure to MPs of three dosages (10, 30, and 80 particles/g-TS), three polymer types (LDPE, PET, and PS), and three branching extents (LDPE, LLDPE, and HDPE) in anaerobic sludge digestion was investigated. Metagenomic results indicated that all variants of MPs resulted in an increase of the relative abundance of ARGs in the digester compared to the control. The abundance of ARGs demonstrated a dosage-dependent relationship within the range from 10 to 80 particles/g-TS, resulting in an increase from 4.5 to 27.9% compared to the control. Branching structure and polymer type influence ARG level in the sludge digester as well. Mechanism studies revealed that LDPE selectively enriched potential ARB and ARGs in the surface biofilm, possibly creating a favorable environment for ARB proliferation and ARG exchange. Furthermore, vertical transfer of ARGs was facilitated by LDPE through increasing bacterial cell proliferation accompanied by the enhancement of relevant functional genes. The elevated abundance of mobile genetic elements (MGEs) and ARGs-carrying plasmids also demonstrated that MGE-mediated horizontal transfer was promoted by LDPE at 80 particles/g-TS. This effect was compounded by increased oxidative stress, cell membrane permeability, and cell cohesion, collectively facilitating horizontal ARG transfer. Consequently, both vertical and horizontal transfer of ARGs could be concurrently promoted by LDPE an in anaerobic sludge digester.

Combined Effects of Micro- and Nanoplastics at the Predicted Environmental Concentration on Functional State of Intestinal Barrier in Caenorhabditis elegans

The possible toxicity caused by nanoplastics or microplastics on organisms has been extensively studied. However, the unavoidably combined effects of nanoplastics and microplastics on organisms, particularly intestinal toxicity, are rarely clear. Here, we employed Caenorhabditis elegans to investigate the combined effects of PS-50 (50 nm nanopolystyrene) and PS-500 (500 nm micropolystyrene) at environmentally relevant concentrations on the functional state of the intestinal barrier. Environmentally, after long-term treatment (4.5 days), coexposure to PS-50 (10 and 15 μg/L) and PS-500 (1 μg/L) resulted in more severe formation of toxicity in decreasing locomotion behavior, in inhibiting brood size, in inducing intestinal ROS production, and in inducting intestinal autofluorescence production, compared with single-exposure to PS-50 (10 and 15 μg/L) or PS-500 (1 μg/L). Additionally, coexposure to PS-50 (15 μg/L) and PS-500 (1 μg/L) remarkably caused an enhancement in intestinal permeability, but no detectable abnormality of intestinal morphology was observed in wild-type nematodes. Lastly, the downregulation of acs-22 or erm-1 expression and the upregulation expressions of genes required for controlling oxidative stress (sod-2, sod-3, isp-1, clk-1, gas-1, and ctl-3) served as a molecular basis to strongly explain the formation of intestinal toxicity caused by coexposure to PS-50 (15 μg/L) and PS-500 (1 μg/L). Our results suggested that combined exposure to microplastics and nanoplastics at the predicted environmental concentration causes intestinal toxicity by affecting the functional state of the intestinal barrier in organisms.

Crystal structure and biochemical analysis of acetylesterase (LgEstI) from Lactococcus garvieae

Esterase, a member of the serine hydrolase family, catalyzes the cleavage and formation of ester bonds with high regio- and stereospecificity, making them attractive biocatalysts for the synthesis of optically pure molecules. In this study, we performed an in-depth biochemical and structural characterization of a novel microbial acetylesterase, LgEstI, from the bacterial fish pathogen Lactococcus garvieae. The dimeric LgEstI displayed substrate preference for the short acyl chain of p-nitrophenyl esters and exhibited increased activity with F207A mutation. Comparative analysis with other esterases indicated that LgEstI has a narrow and shallow active site that may exhibit substrate specificity to short acyl chains. Unlike other esterases, LgEstI contains bulky residues such as Trp89, Phe194, and Trp217, which block the acyl chain channel. Furthermore, immobilized LgEstI retained approximately 90% of its initial activity, indicating its potential in industrial applications. This study expands our understanding of LgEstI and proposes novel ideas for improving its catalytic efficiency and substrate specificity for various applications.

Environmental role of aromatic carboxylesterases

The carboxylesterases (EC 3.1.1.x) are widely distributed and form an important yet diverse group of hydrolases catalysing the ester bond cleavage in a variety of substrates. Besides acting on plant cell wall components like cutin, tannin and feruloyl esters, they are often the first line of defence to metabolize drugs, xenobiotics, pesticides, insecticides and plastic. But for the promiscuity of some carboxylesterases and cutinases, very few enzymes act exclusively on aromatic carboxylic acid esters. Infrequent occurrence of aromatic carboxylesterases suggests that aromatic carboxylesters are inherently more difficult to hydrolyse than the regular carboxylesters because of both steric and polar effects. Naturally occurring aromatic carboxylesters were rare before the anthropogenic activity augmented their environmental presence and diversity. An appraisal of the literature shows that the hydrolysis of aromatic carboxylic esters is a uniquely difficult endeavour and hence deserves special attention. Enzymes to hydrolyse such esters are evolving rapidly in nature. Very few such enzymes are known and they often display much lower catalytic efficiencies. Obviously, the esters of aromatic carboxylic acids, including polyethylene terephthalate waste, pose an environmental challenge. In this review, we highlight the uniqueness of aromatic carboxylesters and then underscore the importance of relevant carboxylesterases.

Coinducible Catabolism of 1-Naphthol via Synergistic Regulation of the Initial Hydroxylase Genes in Sphingobium sp. Strain B2

1-Naphthol, a widely used raw material for organic synthesis, is also a well-known organic pollutant. Due to its high toxicity, 1-naphthol is rarely used by microorganisms as the sole carbon source for growth. In this study, catabolism of 1-naphthol by Sphingobium sp. strain B2 was found to be greatly enhanced by additional supplementation with primary carbon sources (e.g., glucose, maltose, and sucrose), and 1-naphthol was even used as the carbon source for growth when strain B2 cells had been preinduced by both 1-naphthol and glucose. A distinct two-component flavin-dependent monooxygenase, NdcA1A2, was found to be responsible for the initial hydroxylation of 1-naphthol to 1,2-dihydroxynaphthalene, a more toxic compound. Transcriptional levels of ndcA1A2 genes were significantly upregulated when strain B2 cells were cultured with both 1-naphthol and glucose compared to cells cultured with only 1-naphthol or glucose. Two transcriptional regulators, the activator NdcS and the inhibitor NdcR, were found to play key roles in the synergistic regulation of the transcription of the 1-naphthol initial catabolism genes ndcA1A2 IMPORTANCE Cometabolism is a widely observed phenomenon, especially in the field of microbial catabolism of highly toxic xenobiotics. However, the mechanisms of cometabolism are ambiguous, and the roles of the obligately coexisting growth substrates remain largely unknown. In this study, we revealed that the roles of the coexisting primary carbon sources (e.g., glucose) in the enhanced catabolism of the toxic compound 1-naphthol in Sphingobium sp. strain B2 were not solely because they were used as growth substrates to support cell growth but, more importantly, because they acted as coinducers to interact with two transcriptional regulators, the activator NdcS and the inhibitor NdcR, to synergistically regulate the transcription of the 1-naphthol initial catabolism genes ndcA1A2 Our findings provide new insights into the cometabolic mechanism of highly toxic compounds in microorganisms.

Multigenerational effects of polyethylene terephthalate microfibers in Caenorhabditis elegans

Microfibers (MFs) have recently become an increasingly prevalent pollutant in ecosystems and pose a direct threat to organisms and an indirect threat via adsorption of other pollutants. Here, we used Caenorhabditis elegans to study multigenerational effects of polyethylene terephthalate (PET) MFs (diameter 17.4 μm) by observing the maternal generation (P0) to the seventh offspring generation (F7) with continuous MF exposure. Exposure to 250-μm PET MFs decreased locomotion behavior and induced intestinal reactive oxygen species (ROS) in the P0 generation compared with other PET MF sizes. Moreover, no notably negative effects on survival were observed in any generation during continuous exposure to 250-μm PET MFs. However, the reproduction rate clearly decreased in the F2 and F3 generations but gradually recovered in the F4-F7 generations. Developmental abnormalities showed a close relationship with body length. Although some recovery was confirmed, there were significant decreases in body length in the F2-F5 generations. Interestingly, growth inhibition was also observed in the F6 generation without MF exposure. ROS production and dermal damage in the P0-F5 generations might have resulted in the toxicological responses. To the best of our knowledge, this is the first study to provide evidence of multigenerational toxicity of MFs in C. elegans.

Neuronal ERK MAPK signaling in response to low-dose nanopolystyrene exposure by suppressing insulin peptide expression in Caenorhabditis elegans

The responses of different organs are important for organisms against the toxicity of environmental toxicants. So far, the neuronal response to nanoplastic exposure and the underlying mechanisms are still largely unclear. Due to the sensitivity to environmental exposures, we here employed Caenorhabditis elegans as an animal model to examine the role of ERK MAPK signaling pathway in the neurons to regulate the response to nanopolystyrene (100 nm). Nanopolystyrene exposure in the range of μg/L could significantly increase expressions of genes (lin-45, mek-2, and mpk-1) encoding ERK MAPK signaling pathway. Nanopolystyrene at the predicted environmental concentration of 1 μg/L could only significantly increase the mpk-1 expression. Meanwhile, RNAi knockdown of any of these genes caused a susceptibility to nanopolystyrene toxicity. ERK/MPK-1 acted in the neurons to regulate the response to nanopolystyrene. Moreover, three genes (ins-4, ins-39, and daf-28) encoding insulin peptides were identified as the downstream targeted genes of neuronal mpk-1 in regulating the response to nanopolystyrene. In nanopolystyrene exposed nematodes, neuronal RNAi knockdown of ins-4, ins-39, or daf-28 decreased expression of intestinal daf-2 encoding insulin receptor and increased expression of intestinal daf-16 encoding FOXO transcriptional factor. Therefore, the neuronal ERK MAPK signaling responded to nanopolystyrene by modulating the insulin signaling-mediated communication between neurons and intestine in nematodes. Our findings are helpful for understanding the molecular basis of neuronal response to nanopolystyrene in organisms.

Assessment of nanopolystyrene toxicity under fungal infection condition in Caenorhabditis elegans

Due to the potential of release and accumulation in the environment, nanoplastics have attracted an increasing attention. In this study, we investigated the effect of exposure to nanopolystyrene (30 nm) in nematode Caenorhabditis elegans after the fungal infection. After Candida albicans infection, exposure to nanopolystyrene (10 and 100 μg/L) for 24-h could cause the more severe toxicity on lifespan and locomotion behavior compared with fungal infection alone. The more severe activation of oxidative stress and suppression of SOD-3:GFP expression and mitochondrial unfolded protein response (mt UPR) were associated with this observed toxicity enhancement induced by nanopolystyrene exposure. Moreover, the more severe C. albicans colony formation and suppression of innate immune response as indicated by the alteration in expression of anti-microbial genes (abf-2, cnc-4, cnc-7, and fipr-22/23) further contributed to the formation of this toxicity enhancement induced by nanopolystyrene exposure. Our results demonstrated that short-term exposure to nanopolystyrene in the range of μg/L potentially enhances the adverse effects of fungal infection on organisms.

A Rapid Method for the Selection of Amidohydrolases from Metagenomic Libraries by Applying Synthetic Nucleosides and a Uridine Auxotrophic Host

In this study, the development of a rapid, high-throughput method for the selection of amide-hydrolysing enzymes from the metagenome is described. This method is based on uridine auxotrophic Escherichia coli strain DH10B ∆pyrFEC and the use of N4-benzoyl-2’-deoxycytidine as a sole source of uridine in the minimal microbial M9 medium. The approach described here permits the selection of unique biocatalysts, e.g., a novel amidohydrolase from the activating signal cointegrator homology (ASCH) family and a polyethylene terephthalate hydrolase (PETase)-related enzyme.