Biocatalytic Degradation of Parabens Mediated by Cell Surface Displayed Cutinase

The association between estrogenic activity evolution and the formation of different products during the photochemical transformation of parabens in water

Photochemical transformation is a critical factor influencing the environmental fate of pharmaceutical and personal care products in aquatic ecosystems. However, the relationship between toxicity evolution and the formation of various transformation products has been seldom explored. This study investigates the behavior and changes in estrogenic activity during the photochemical transformation of a series of typical endocrine-disrupting parabens (PBs), focusing on the effects of increasing alkyl-chain length (MPB, EPB, PPB and BPB). Based on MS/MS analysis, four types of transformation products were identified: (1) p-hydroxybenzoic acid (HB), which exhibits no estrogenic activity; (2) hydroxylated products (OH-PBs); (3) dimer products formed between HB and PBs (HB-PBs); and (4) dimer products formed from identical PBs (PBs-PBs), comprising three distinct isomers. In the absence of standard sample, OH-PBs were synthesized and their estrogenic activity was evaluated using a yeast two-hybrid reporter assay. The EC50 values were determined to be <1 × 10-3 M for OH-MPB, 2.05 × 10-4 M for OH-EPB, 5.05 × 10-5 M for OH-PPB, and 1.89 × 10-5 M for OH-BPB. These indicate that the estrogenic activity of OH-PBs is one order of magnitude lower than that of the corresponding PBs. Both HB-PBs and the three isomers of PBs-PBs exhibited significantly higher estrogenic activities than their corresponding parent compounds, increasing 9 - 14 and 32 - 184 times, respectively, based on theoretical calculations. Among the three PBs-PBs isomers, the highest estrogenic activity was observed in the ether dimer, followed by the biphenyl dimers. Consistent with the parent compounds, the estrogenic activities of OH-PBs, HB-PBs, and PBs-PBs increased with the length of the alkyl-chain. The estrogenic activity of MPB and EPB followed an overall downward trend during the photochemical transformation, whereas PPB and BPB remained stable initially before declining rapidly. This behavior was associated with the contributions of toxic transformation products. These findings elucidate the relationship between molecular structure, transformation products, and estrogenic activity, highlighting the importance of understanding estrogenic activity evolution during the photochemical transformation of PBs.

Fusarium as a promising fungal genus with potential application in bioremediation for pollutants mitigation: A review

Fusarium is genetically diverse and widely distributed geographically. It is one of the genera with more endophytes (which cause no damage to the host plants). This review highlights the capability of Fusarium species to degrade environmental pollutants and describes the biodegradation pathways of some of the emerging environmental contaminants. Some Fusarium species use metabolic strategies enabling them to efficiently mineralize high concentrations of toxic environmental pollutants. These fungi can degrade hydrocarbons, pesticides, herbicides, dyes, pharmaceutical compounds, explosives, plastics, and plastic additives, among other pollutants, and possess high metal biosorption capabilities. According to data from consulted reports, Fusarium strains showed a percentage of biodegradation of a variety of contaminants ranging between 30 % and 100 % for different tested concentrations (from 1 mg to 10 g/L) in a time range between 10 h and 90 d. Enzymes such as esterase, cutinase, laccase, lignin peroxidase, manganese peroxidase, dehydrogenase, lipase, dioxygenase, and phosphoesterase were detected during the pollutant biodegradation process. Fusarium oxysporum, Fusarium solani, and Fusarium culmorum are the most studied species of this genus. Owing to their metabolic versatility, these fungal species and their enzymes represent promising tools for bioremediation applications to mitigate the adverse effects of environmental pollution.

Yeast surface display technology: Mechanisms, applications, and perspectives

Microbial cell surface display technology, which relies on genetically fusing heterologous target proteins to the cell wall through fusion with cell wall anchor proteins, has emerged as a promising and powerful method with diverse applications in biotechnology and biomedicine. Compared to classical intracellular or extracellular expression (secretion) systems, the cell surface display strategy stands out by eliminating the necessity for enzyme purification, overcoming substrate transport limitations, and demonstrating enhanced activity, stability, and selectivity. Unlike phage or bacterial surface display, the yeast surface display (YSD) system offers distinct advantages, including its large cell size, ease of culture and genetic manipulation, the use of generally regarded as safe (GRAS) host cell, the ability to ensure correct folding of complex eukaryotic proteins, and the potential for post-translational modifications. To date, YSD systems have found widespread applications in protein engineering, waste biorefineries, bioremediation, and the production of biocatalysts and biosensors. This review focuses on detailing various strategies and mechanisms for constructing YSD systems, providing a comprehensive overview of both fundamental principles and practical applications. Finally, the review outlines future perspectives for developing novel forms of YSD systems and explores potential applications in diverse fields.

Yeast Surface-Displayed Quenchbody as a Novel Whole-Cell Biosensor for One-Step Detection of Influenza A (H1N1) Virus

Timely surveillance of airborne pathogens is essential to preventing the spread of infectious diseases and safeguard human health. Methods for sensitive, efficient, and cost-effective detection of airborne viruses are needed. With advances in synthetic biology, whole-cell biosensors have emerged as promising platforms for environmental monitoring and medical diagnostics. However, the current design paradigm of whole-cell biosensors is mostly based on intracellular detection of analytes that can transport across the cell membrane, which presents a critical challenge for viral pathogens and large biomolecules. To address this challenge, we developed a new type of whole-cell biosensor by expressing and displaying VHH-based quenchbody (Q-body) on the surface of the yeast Saccharomyces cerevisiae for simple one-step detection of influenza A (H1N1) virus. Seventeen VHH antibody fragments targeting the hemagglutinin protein H1N1-HA were displayed on the yeast cells and screened for the H1N1-HA binding affinity. The functionally displayed VHHs were selected to create surface-displayed Q-body biosensors. The surface-displayed Q-body exhibiting the highest quenching and dequenching efficiency was identified. The biosensor quantitatively detected H1N1-HA in a range from 0.5 to 16 μg/mL, with a half-maximal concentration of 2.60 μg/mL. The biosensor exhibited high specificity for H1N1-HA over other hemagglutinin proteins from various influenza A virus subtypes. Moreover, the biosensor succeeded in detecting the H1N1 virus at concentrations from 2.4 × 104 to 1.5 × 107 PFU/mL. The results from this study demonstrated a new whole-cell biosensor design that circumvents the need for transport of analytes into biosensor cells, enabling efficient detection of the target virus particles.

Characterizing an amidase and its operon from actinomycete bacteria responsible for paraben catabolism

Hydrazidase from Microbacterium hydrocarbonoxydans was revealed to catalyze synthetic hydrazide compounds, enabling the bacteria to grow with them as a sole carbon source, but natural substrates have remained unknown. In this study, kinetic analyses of hydrazidase with parabens showed that the compounds can be substrates. Then, methylparaben induced gene expressions of the operon containing hydrazidase and ABC transporter, and the compound as a sole carbon source was able to grow the bacteria. Furthermore, homology search was carried out revealing that several actinomycetes possess hydrazidase homologs in the operon. Among those bacteria, an amidase from Pseudonocardia acaciae was subjected to a kinetic analysis and a structure determination revealing similar but not identical to those of hydrazidase. Since parabens are reported to exist in plants and soil, and several actinomycetes code the homologous operon, the enzymes with those operons may play a physiologically important role for bacterial survival with use of parabens.

Substrate Characterization for Hydrolysis of Multiple Types of Aromatic Esters by Promiscuous Aminopeptidases

Synthetic aromatic esters, widely employed in agriculture, food, and chemical industries, have become emerging environmental pollutants due to their strong hydrophobicity and poor bioavailability. This study attempted to address this issue by extracellularly expressing the promiscuous aminopeptidase (Aps) from Pseudomonas aeruginosa GF31 in B. subtilis, achieving an impressive enzyme activity of 13.7 U/mg. Notably, we have demonstrated, for the first time, the Aps-mediated degradation of diverse aromatic esters, including but not limited to pyrethroids, phthalates, and parabens. A biochemical characterization of Aps reveals its esterase properties and a broader spectrum of substrate profiles. The degradation rates of p-nitrobenzene esters (p-NB) with different side chain structures vary under the action of Aps, showing a preference for substrates with relatively longer alkyl side chains. The structure-dependent degradability aligns well with the binding energies between Aps and p-NB. Molecular docking and enzyme-substrate interaction elucidate that hydrogen bonding, hydrophobic interactions, and π-π stacking collectively stabilize the enzyme-substrate conformation, promoting substrate hydrolysis. These findings provide new insights into the enzymatic degradation of aromatic ester pollutants, laying a foundation for the further development and modification of promiscuous enzymes.

Estrogenic disruption effects and formation mechanisms of transformation products during photolysis of preservative parabens

The ubiquitous presence of emerging contaminants (ECs) in the environment and their associated adverse effects has raised concerns about their potential risks. The increased toxicity observed during the environmental transformation of ECs is often linked to the formation of their transformation products (TPs). However, comprehension of their formation mechanisms and contribution to the increased toxicity remains an unresolved challenge. To address this gap, by combining quantum chemical and molecular simulations with photochemical experiments in water, this study investigated the formation of TPs and their molecular interactions related to estrogenic effect using the photochemical degradation of benzylparaben (BZP) preservative as a representative example. A non-targeted analysis was carried out and three previously unknown TPs were identified during the transformation of BZP. Noteworthy, two of these novel TPs, namely oligomers BZP-o-phenol and BZP-m-phenol, exhibited higher estrogenic activities compared to the parent BZP. Their IC50 values of 0.26 and 0.50 μM, respectively, were found to be lower than that of the parent BZP (6.42 μM). The binding free energies (ΔGbind) of BZP-o-phenol and BZP-m-phenol (-29.71 to -23.28 kcal·mol-1) were lower than that of the parent BZP (-20.86 kcal·mol-1), confirming their stronger binding affinities toward the estrogen receptor (ER) α-ligand binding domain. Subsequent analysis unveiled that these hydrophobic residues contributed most favorably to ER binding, with van der Waals interactions playing a significant role. In-depth examination of the formation mechanisms indicated that these toxic TPs primarily originated from the successive cleavage of ester bonds (OCH2C6H5 and COO group), followed by their combination with BZP*. This study provides valuable insight into the mechanisms underlying the formation of toxic TPs and their binding interactions causing the endocrine-disrupting effects. It offers a crucial framework for elucidating the toxicological patterns of ECs with similar structures.

Engineering biomaterials for the recovery of rare earth elements

The escalating global demand for rare earth elements (REEs) and the overabundance of REE-containing waste require innovative technologies for REE recovery from waste to achieve a sustainable supply of REEs while reducing the environmental burden. Biosorption mediated by peptides or proteins has emerged as a promising approach for selective REE recovery. To date, multiple peptides and proteins with high REE-binding affinity and selectivity have been discovered, and various strategies are being exploited to engineer robust and reusable biosorptive materials for selective REE recovery. This review highlights recent advances in discovering and engineering peptides and proteins for REE recovery. Future research prospects and challenges are also discussed.

Recent advances in the biodegradation of polyethylene terephthalate with cutinase-like enzymes

Polyethylene terephthalate (PET) is a synthetic polymer in the polyester family. It is widely found in objects used daily, including packaging materials (such as bottles and containers), textiles (such as fibers), and even in the automotive and electronics industries. PET is known for its excellent mechanical properties, chemical resistance, and transparency. However, these features (e.g., high hydrophobicity and high molecular weight) also make PET highly resistant to degradation by wild-type microorganisms or physicochemical methods in nature, contributing to the accumulation of plastic waste in the environment. Therefore, accelerated PET recycling is becoming increasingly urgent to address the global environmental problem caused by plastic wastes and prevent plastic pollution. In addition to traditional physical cycling (e.g., pyrolysis, gasification) and chemical cycling (e.g., chemical depolymerization), biodegradation can be used, which involves breaking down organic materials into simpler compounds by microorganisms or PET-degrading enzymes. Lipases and cutinases are the two classes of enzymes that have been studied extensively for this purpose. Biodegradation of PET is an attractive approach for managing PET waste, as it can help reduce environmental pollution and promote a circular economy. During the past few years, great advances have been accomplished in PET biodegradation. In this review, current knowledge on cutinase-like PET hydrolases (such as TfCut2, Cut190, HiC, and LCC) was described in detail, including the structures, ligand-protein interactions, and rational protein engineering for improved PET-degrading performance. In particular, applications of the engineered catalysts were highlighted, such as improving the PET hydrolytic activity by constructing fusion proteins. The review is expected to provide novel insights for the biodegradation of complex polymers.

Direct Yeast Surface Codisplay of Sequential Enzymes with Complementary Anchor Motifs: Enabling Enhanced Glycosylation of Natural Products

Yeast surface display is an appealing technique for constructing multienzyme cascades. This technique is commonly achieved using a scaffold for the ordered arrangement of various enzymes. However, this method is typically complicated because scaffold use may engender extra metabolic burden on the cell host. Here, we established a direct yeast surface codisplay strategy by employing two complementary anchor motifs, Agα1 and Pir1. These motifs allow for the codisplay of sequential uridine diphosphate-glycosyltransferase (UGT) and sucrose synthase (SUS) on the surface of Pichia pastoris (syn. Komagataella phaffii) for the glycosylation of natural products. We manipulated the displayed stoichiometry, amount, and assembly order of UGT and SUS by coupling them with anchor motifs. Furthermore, their effect on enzyme activity was thoroughly investigated. The surface-codisplayed strain UGT-Pir-SUS-Agα exhibited greater thermostability than the single-displayed strains and their free counterparts. Moreover, the strain UGT-Pir-SUS-Agα was successfully applied to glycyrrhetinic acid (GA) glycosylation to produce GA-3-O-Glc, with sucrose being the sugar donor in this process. This generated 7.5- to 20- and 5.3-fold higher GA-3-O-Glc concentration compared with the free counterparts (enzyme mass loading of 20-fold in excess) and mixed single-displayed strains of UGT-Agα and SUS-Pir, respectively. This increase was due to the improved biochemical properties and substrate channeling effect of strain UGT-Pir-SUS-Agα. This controllable direct surface codisplay strategy, based on complementary anchor motifs, is readily extendable to other enzyme cascades.

Saccharomyces cerevisiae cell surface display technology: Strategies for improvement and applications

Microbial cell surface display technology provides a powerful platform for engineering proteins/peptides with enhanced properties. Compared to the classical intracellular and extracellular expression (secretion) systems, this technology avoids enzyme purification, substrate transport processes, and is an effective solution to enzyme instability. Saccharomyces cerevisiae is well suited to cell surface display as a common cell factory for the production of various fuels and chemicals, with the advantages of large cell size, being a Generally Regarded As Safe (GRAS) organism, and post-translational processing of secreted proteins. In this review, we describe various strategies for constructing modified S. cerevisiae using cell surface display technology and outline various applications of this technology in industrial processes, such as biofuels and chemical products, environmental pollution treatment, and immunization processes. The approaches for enhancing the efficiency of cell surface display are also discussed.

Establishment of a Novel Cell Surface Display Platform Based on Natural "Chitosan Beads" of Yeast Spores

Cell surface display technology, which expresses and anchors proteins on the surface of microbial cells, has broad application prospects in many fields, such as protein library screening, biocatalysis, and biosensor development. However, traditional cell surface display systems have disadvantages: the molecular weight of phage display proteins cannot be too large; bacterial display lacks the post-translational modification process for eukaryotic proteins; yeast display is prone to excessive protein glycosylation and misfolding of multisubunit proteins; and the compatibility of Bacillus subtilis spore display needs to be further improved. Therefore, it is extremely valuable to develop an efficient surface display platform with strong universality and stress resistance properties. Although yeast surface display systems have been extensively investigated, the establishment of a surface display platform using yeast spores has rarely been reported. In this study, a novel cell surface display platform based on natural "chitosan beads" of yeast spores was developed. The target protein in fusion with the chitosan affinity protein (CAP) exhibited strong binding capability with "chitosan beads" of yeast spores in vitro and in vivo. Moreover, this protein display system showed highly preferable enzymatic properties and stability. As an example, the displayed LXYL-P1-2-CAP demonstrated high thermostability and reusability (60% of the initial activity after seven cycles of reuse), high storage stability (75% of original activity after 8 weeks), and excellent tolerance to a concentration up to 75% (v/v) organic reagents. To prove the practicability of this surface display system, the semisynthesis of paclitaxel intermediate was demonstrated and its highest conversion rate was 92% using 0.25 mM substrate. This study provides a novel and useful platform for the surface display of proteins, especially for multimeric macromolecular proteins of eukaryotic origin.

Tyrosinase-functionalized polyhydroxyalkanoate bio-beads as a novel biocatalyst for degradation of bisphenol analogues

Bisphenol compounds are emerging contaminants of high concerns with known endocrine-disrupting effects. Biocatalysis provides a green chemistry alternative for advanced treatment in water reclamation. This study createda novel biocatalyst through genetically immobilizing the Bacillus megaterium tyrosinase enzyme (BmTyr) on the surface ofself-assembled polyhydroxyalkanoate (PHA) biopolymer beads (termed PHA-BmTyr) by using synthetic biology techniques and demonstrated one-pot in vivo production of the biocatalyst for effective degradation and detoxification of various bisphenol analogues for the first time. The degradation pathway of bisphenols was determined to be mediated by the monophenolase and diphenolase activity of BmTyr. Notably, biocatalytic bisphenol degradation by PHA-BmTyr could substantially reduce or eliminate estrogenic activity of the contaminants, and the degradation products had remarkably lower acute and chronic toxicity than their parent compounds. Furthermore, the PHA-BmTyr biocatalyst had high reusability for multiple bisphenol degradation reaction cycles and showed excellent stability that retained 100% and 86.6% of the initial activity when stored at 4 °C and room temperature, respectively for 30 days. Also, the PHA-BmTyr biocatalyst could efficiently degrade bisphenol analogues in real wastewater effluent matrix. This study provides a promising approach to develop innovative biocatalysis technologies for sustainable water reclamation.

The curious case of methylparaben: Anthropogenic contaminant or natural origin?

The widespread use of methylparaben as a preservative has caused increased exposure to natural aquatic systems in recent decades. However, current studies have suggested that exposure to this compound can result in endocrine disrupting effects, raising much concern regarding its environmental impact. In contast, methylparaben has also been found to be part of the metabolome of some organisms, prompting the question as to whether this compound may be more natural than previously assumed. Through a combination of field studies investigating the natural presence of methylparaben across different taxa, and a 54-day microcosm experiment examining the bioaccumulation and movement of methylparaben across different life stages of aquatic insects (order Trichoptera), our results offer evidence suggesting the natural origin of methylparaben in aquatic and terrestrial biota. This study improves our understanding of the role and impact this compound has on biota and challenges the current paradigm that methylparaben is exclusively a harmful anthropogenic contaminant. Our findings highlight the need for further research on this topic to fully understand the origin and role of parabens in the environment which will allow for a comprehensive understanding of the extent of environmental contamination and result in a representative assessment of the environmental risk that may pose.

Toxicity and removal of parabens from water: A critical review

Parabens are biocides used as preservatives in food, cosmetics and pharmaceuticals. They possess antibacterial and antifungal activity due to their ability to disrupt cell membrane and intracellular proteins, and cause changes in enzymatic activity of microbial cells. Water, one of our most valuable natural resource, has become a huge reservoir for parabens. Halogenated parabens from chlorination/ozonation of water contaminated with parabens have shown to be even more persistent in water than other types of parabens. Unfortunately, there is dearth of data on their (halogenated parabens) presence and fate in groundwater which serves as a major source of drinking water for a huge population in developing countries. An attempt to neglect the presence of parabens in water will expose man to it through ingestion of contaminated food and water. Although there are reviews on the occurrence, fate and behaviour of parabens in the environment, they largely omit toxicity and removal aspects. This review therefore, presents recent reports on the acute and chronic toxicity of parabens, their estrogenic agonistic and antagonistic activity and also their relationship with antimicrobial resistance. This article further X-rays several techniques that have been employed for the removal of parabens in water and their drawbacks including adsorption, biodegradation, membrane technology and advanced oxidation processes (AOPs). The heterogeneous photocatalytic process (one of the AOPs) appears to be more favoured for removal of parabens due to its ability to mineralize parabens in water. However, more work is needed to improve this ability of heterogeneous photocatalysts. Perspectives that will be relevant for future scientific studies and which will drive policy shift towards the presence of parabens in our drinking waters are also offered. It is hoped that this review will elicit some spontaneous actions from water professionals, scientists and policy makers alike that will provide more data, effective technologies, and adaptive policies that will address the growing threat of the presence of parabens in our environment with respect to human health.

Magnetic Nanoplatforms for Covalent Protein Immobilization Based on Spy Chemistry

Immobilization of proteins on magnetic nanoparticles (MNPs) is an effective approach to improve protein stability and facilitate separation of immobilized proteins for repeated use. Herein, we exploited the efficient SpyTag-SpyCatcher chemistry for conjugation of functional proteins onto MNPs and established a robust magnetic-responsive nanoparticle platform for protein immobilization. To maximize the loading capacity and achieve outstanding water dispersity, the SpyTag peptide was incorporated into the surface-charged polymers of MNPs, which provided abundant active sites for Spy chemistry while maintaining excellent colloidal stability in buffer solution. Conjugation between enhanced green fluorescence protein (EGFP)-SpyCatcher-fused proteins and SpyTag-functionalized MNPs was efficient at ambient conditions without adding enzymes or chemical cross-linkers. Benefiting from the excellent water dispersity and interface compatibility, the surface Spy reaction has fast kinetics, which is comparable to that of the solution Spy reaction. No activity loss was observed on EGFP after conjugation due to the site-selective nature of Spy chemistry. The immobilization process of EGFP on MNPs was highly specific and robust, which was not affected by the presence of other proteins and detergents, such as bovine serum albumin and Tween 20. The MNP platform was demonstrated to be protective to the conjugated EGFP and significantly improved the shelf life of immobilized proteins. In addition, experiments confirmed the retained magnetophoresis of the MNP after protein loading, demonstrating fast MNP recovery under an external magnetic field. This MNP is expected to provide a versatile and modular platform to achieve effective and specific immobilization of other functional proteins, enabling easy reuse and storage.

The degradation of paraben preservatives: Recent progress and sustainable approaches toward photocatalysis

Parabens are a class of compounds primarily used as antimicrobial preservatives in pharmaceutical products, cosmetics, and foodstuff. Their widely used field leads to increasing concentrations detected in various environmental matrices like water, soil, and sludges, even detected in human tissue, blood, and milk. Treatment techniques, including chemical advanced oxidation, biological degradation, and physical adsorption processes, have been widely used to complete mineralization or to degrade parabens into less complicated byproducts. All kinds of processes were reviewed to give a completed picture of parabens removal. In light of these treatment techniques, advanced photocatalysis, which is emerging rapidly and widely as an economical, efficient, and environmentally-friendly technique, has received considerable attention. TiO₂-based and non-TiO₂-based photocatalysts play an essential role in parabens degradation. The effect of experimental parameters, such as the concentration of targeted parabens, concentration of photocatalyst, reaction time, and initial solution pH, even the presence of radical scavengers, are surveyed and compared from the literature. Some representative parabens such as methylparaben, propylparaben, and benzylparaben have been successfully studied the reaction pathways and their intermediates in their degradation process. As reported in the literature, the degradation of parabens involves the production of highly reactive species, mainly hydroxyl radicals. These reactive radicals would attack the paraben preservatives, break, and finally mineralize them into simpler inorganic and nontoxic molecules. Concluding perspectives on the challenges and opportunities for photocatalysis toward parabens remediation are also intensively highlighted.

Synthesis, Enzymatic Degradation, and Polymer-Miscibility Evaluation of Nonionic Antimicrobial Hyperbranched Polyesters with Indole or Isatin Functionalities

Most macromolecular antimicrobials are ionic and thus lack miscibility/compatibility with nonionic substrate materials. In this context, nonionic hyperbranched polyesters (HBPs) with indole or isatin functionality were rationally designed, synthesized, and characterized. Antimicrobial disk diffusion assay indicated that these HBPs showed significant antibacterial activity against 8 human pathogenic bacteria compared to small molecules with indole or isatin groups. According to DSC measurements, up to 20% indole-based HBP is miscible with biodegradable polyesters (polyhydroxybutyrate or polycaprolactone), which can be attributed to the favorable hydrogen bonding between the N–H moiety of indole and the C=O of polyesters. HBPs with isatin or methylindole were completely immiscible with the same matrices. None of the HBPs leaked out from plastic matrix after being immersed in water for 5 days. The incorporation of indole into HBPs as well as small molecules facilitated their enzymatic degradation with PETase from Ideonella sakaiensis, while isatin had a complex impact. Molecular docking simulations of monomeric molecules with PETase revealed different orientations of the molecules at the active site due to the presence of indole or isatin groups, which could be related to the observed different enzymatic degradation behavior. Finally, biocompatibility analysis with a mammalian cell line showed the negligible cytotoxic effect of the fabricated HBPs.

IsPETase Is a Novel Biocatalyst for Poly(ethylene terephthalate) (PET) Hydrolysis

Poly(ethylene terephthalate) (PET) is one of the most widely used synthetic polyesters, but also a major cause of plastic pollution. Because the chemical degradation of PET would be uneconomical and rather burdensome, considerable efforts have been devoted to exploring enzymatic processes for the disposal of PET waste. Many PET-hydrolyzing enzymes have been reported in recent decades, some of which demonstrate excellent potential for industrial applications. This review sets out to summarize the state of investigation into IsPETase, a cutinase-like enzyme from Ideonella sakaiensis possessing ability to degrade crystalline PET, and to gain further insight into the structure-function relationship of IsPETase. Benefiting from the continuing identification of novel cutinase-like proteins and growing availability of the engineered IsPETase, we may anticipate future developments in this type of enzyme would generate suitable biocatalyst for industrial use.

Yeast cell surface display of bacterial PET hydrolase as a sustainable biocatalyst for the degradation of polyethylene terephthalate

Enzymatic hydrolysis of polyethylene terephthalate (PET) is considered to be an environmentally friendly method for the recycling of plastic waste. Recently, a bacterial enzyme named IsPETase was found in Ideonella sakaiensis with the ability to degrade amorphous PET at ambient temperature suggesting its possible use in recycling of PET. However, applying the purified IsPETase in large-scale PET recycling has limitations, i.e., a complicated production process, high cost of single-use, and instability of the enzyme. Yeast cell surface display has proven to be an effectual alternative for improving enzyme degradation efficiency and realizing industrial applications. This chapter deals with the construction and application of a whole-cell biocatalyst by displaying IsPETase on the surface of yeast (Pichia pastoris) cells.

Cell-surface engineering of yeasts for whole-cell biocatalysts

Due to the unique advantages comparing with traditional free enzymes and chemical catalysis, whole-cell biocatalysts have been widely used to catalyze reactions effectively, simply and environment friendly. Cell-surface display technology provides a novel and effective approach for improved whole-cell biocatalysts expressing heterologous enzymes on the cell surface. They can overcome the substrate transport limitation of the intracellular expression and provide the enzymes with enhanced properties. Among all the host surface-displaying microorganisms, yeast is ideally suitable for constructing whole cell-surface-displaying biocatalyst, because of the large cell size, the generally regarded as safe (GRAS) status, and the perfect post-translational processing of secreted proteins. Yeast cell-surface display system has been a promising and powerful method for development of novel and improved engineered biocatalysts. In this review, the characterization and principles of yeast cell-surface display and the applications of yeast cell-surface display in engineered whole-cell biocatalysts as well as the improvement of the enzyme efficiency are summarized and discussed.

Unexpected culprit of increased estrogenic effects: Oligomers in the photodegradation of preservative ethylparaben in water

Widespread occurrence of emerging organic contaminants (EOCs) in water have been explicitly associated with adverse effects on human health, therefore representing a major risk to public health. Especially the increased toxicity is frequently observed during the photodegradation of EOCs in natural water, and even wastewater treatment plants. However, the culprit of increased toxicity and formation mechanism has yet to be recognized regarding the estrogenic activity. In this study, by combining laboratory experiments with quantum chemical calculations, the induction of human estrogenic activity was investigated using the yeast two-hybrid reporter assay during the photodegradation of preservatives ethylparaben (EP), along with identification of toxic products and formation mechanisms. Results showed that the increase in estrogenic effect was induced by photochemically generated oligomers, rather than the expected OH-adduct. The maximum estrogenic activity corresponded to the major formation of oligomers, while OH-adducts were less than 12%. Two photochemically generated oligomers were found to contribute to estrogenic activity, produced from the cleavage of excited triplet state molecules and subsequent radical-radical reactions. Computational toxicology results showed that the increased estrogenic activity was attributed to oligomer [4-Hydroxy-isophthalic acid 1-ethyl ester 3-(4-hydroxy-phenyl)] and its EC₅₀ was lower than that of the parent EP. In contrast, OH-adducts exhibited higher EC₅₀ values than the parent EP, while still possessing estrogenic activity. Therefore, more attention should be paid to these photodegradation products of EOCs, including OH-adducts.

Efficient biodegradation of highly crystallized polyethylene terephthalate through cell surface display of bacterial PETase

Polyethylene terephthalate (PET) is one of the most widely used plastics in the world. Accumulation of the discarded PET in the environment is creating a global environmental problem. Recently, a bacterial enzyme named PETase was found to have the novel ability to degrade the highly crystallized PET. However, the enzymatic activity of native PETase is still low limiting its possible use in recycling of PET. In this study, we developed a whole-cell biocatalyst by displaying PETase on the surface of yeast (Pichia pastoris) cell to improve its degradation efficiency. Our data shows that PETase could be functionally displayed on the yeast cell with enhanced pH and thermal stability. The turnover rate of the PETase-displaying yeast whole-cell biocatalyst towards highly crystallized PET dramatically increased about 36-fold compared with that of purified PETase. Furthermore, the whole-cell biocatalyst showed stable turnover rate after seven repeated use and under some chemical/solvent conditions, and its ability to degrade different commercial highly crystallized PET bottles. Our results reveal that PETase-displaying whole-cell biocatalyst affords a promising route for efficient biological recycling of PET.