Engineering Biocatalytic and Biosorptive Materials for Environmental Applications

Flow cytometry-based high-throughput screening of synthetic peptides for palladium adsorption

Conventionally, the measurement of metal ion adsorption capacity in biosorbent relies on expensive and time-consuming ICP-OES technique. Herein, a semi-quantitative method to measure Pd(II) adsorption capacity of single cells has been presented by analyzing side scatter (SSC) intensity in flow cytometry. Within the sensitive range and applicable conditions, excellent linearity correlation (R2 ranges from 0.89 to 0.96) between the amount of Pd(II) absorbed on yeast and the fold increase in SSC intensity has been observed. Using this method, six strains with high Pd adsorption capacities have sorted from a yeast library with metal-binding peptides displayed (up to 107 strains) based on SSC signal intensity. The optimal peptide (EF1) displayed on yeast and E. coli surface demonstrated Pd adsorption improvements of ∼32% and ∼200%, respectively. In summary, our study proposes an alternative high-throughput method for analyzing the Pd(II) adsorption capacity of individual yeast cells, enabling the screening of specific peptides/proteins with high Pd(II) affinity from extensive libraries.

Structural Regulation of Photocatalyst to Optimize Hydroxyl Radical Production Pathways for Highly Efficient Photocatalytic Oxidation

Ring-opening of phenol in wastewater is the pivotal step in photocatalytic degradation. The highly selective generation of catalytical active species (•OH) to facilitate this process presents a significant scientific challenge. Therefore, a novel approach for designing photocatalysts with single-atom containment in metal-covalent organic frameworks (M-COFs) is proposed. The selection of imine-linked COFs containing abundant N and O-chelate sites provides a solid foundation for anchoring metal atom. These dispersed metal atom possess rapid accumulation and transfer capabilities for photogenerated electrons, while the periodic π-conjugated structure in 2D-COFs establishes an effective platform. Additionally, the Lewis acid properties of imine bonds in COFs can enhance the adsorption capacity toward gases with Lewis base properties, such as O2 and N2 . It is demonstrated that the Pd2+ @Tp-TAPT, designed based on this concept, exhibits efficient oxygen adsorption and follows the reaction pathway of O2 →•O2 - →H2 O2 →•OH with high selectivity, thereby achieving completely degradation of refractory phenol through photocatalysis within 10 min. It is anticipated that the selective generation of catalytic active species via advanced material design concepts will serve as a significant reference for achieving precise material catalysis in the future.

Microbial bioprocess performance in nanoparticle-mediated composting

Microbial composting is one of the most cost-effective techniques for degradation, remediation, nutrition, etc. Currently, there is faster growth and development in nanotechnology in different sectors. This development leads nanoparticles (NPs) to enter into the composts in different ways. First, unintentional entry of NPs into the composts via: waste discharge, buried solid waste, surface runoff, direct disposal into wastes (consumer goods, food, pharmaceuticals, and personal care products). Second, intentional mediation of the NPs in the composting process is a novel approach developed to enhance the degradation rate of wastes and as a nutrient for plants. The presence of NPs in the composts can cause nanotoxicity. Conversely, their presence might also be beneficial, such as soil reclamations, degradation, etc. Alternatively, metal NPs are also helpful for all living organisms, including microorganisms, in various biological processes, such as DNA replication, precursor biosynthesis, respiration, oxidative stress responses, and transcription. NPs show exemplary performance in multiple fields, whereas their role in composting process is worth studying. Consequently, this article aids the understanding of the role of NPs in the composting process and how far their presence can be beneficial. This article reviews the significance of NPs in: the composting process, microbial bioprocess performance during nano composting, basic life cycle assessment (LCA) of NP-mediated composting, and mode of action of the NPs in the soil matrix. This article also sheds insight on the notion of nanozymes and highlights their biocatalytic characterization, which will be helpful in future composting research.

Safe Production Strategies for Soil-Covered Cultivation of Morel in Heavy Metal-Contaminated Soils

Morel is a popular edible mushroom with considerable medicinal and economic value which has garnered global popularity. However, the increasing heavy metal (HM) pollution in the soil presents a significant challenge to morels cultivation. Given the susceptibility of morels to HM accumulation, the quality and output of morels are at risk, posing a serious food safety concern that hinders the development of the morel industry. Nonetheless, research on the mechanism of HM enrichment and mitigation strategies in morel remains scarce. The morel, being cultivated in soil, shows a positive correlation between HM content in its fruiting body and the HM content in the soil. Therefore, soil remediation emerges as the most practical and effective approach to tackle HM pollution. Compared to physical and chemical remediation, bioremediation is a low-cost and eco-friendly approach that poses minimal threats to soil composition and structure. HMs easily enriched during morels cultivation were examined, including Cd, Cu, Hg, and Pb, and we assessed soil passivation technology, microbial remediation, strain screening and cultivation, and agronomic measures as potential approaches for HM pollution prevention. The current review underscores the importance of establishing a comprehensive system for preventing HM pollution in morels.

Recent Advances in the Biocatalytic Mitigation of Emerging Pollutants: A Comprehensive Review

The issue of environmental pollution has been worsened by the emergence of new contaminants whose morphology is yet to be fully understood. Several techniques have been adopted to mitigate the pollution effects of these emerging contaminants, and bioremediation involving plants, microbes, or enzymes has stood out as a cost-effective and eco-friendly approach. Enzyme-mediated bioremediation is a very promising technology as it exhibits better pollutant degradation activity and generates less waste. However, this technology is subject to challenges like temperature, pH, and storage stability, in addition to recycling difficulty as it is arduous to isolate them from the reaction media. To address these challenges, the immobilization of enzymes has been successfully applied to ameliorate the activity, stability, and reusability of enzymes. Although this has significantly increased the uses of enzymes over a wide range of environmental conditions and facilitated the use of smaller bioreactors thereby saving cost, it still comes with additional costs for carriers and immobilization. Additionally, the existing immobilization methods have their individual limitations. This review provides state-of-the-art information to readers focusing on bioremediation using enzymes. Different parameters such as: the sustainability of biocatalysts, the ecotoxicological evaluation of transformation contaminants, and enzyme groups used were reviewed. The efficacy of free and immobilized enzymes, materials and methods for immobilization, bioreactors used, challenges to large-scale implementation, and future research needs were thoroughly discussed.

Emerging enzyme surface display systems for waste resource recovery

The current century marks an inflection point for human progress, as the developed world increasingly comes to recognize that the ecological and socioeconomic impacts of resource extraction must be balanced with more sustainable modes of growth that are less reliant on non-renewable sources of energy and materials. This has opened a window of opportunity for cross-sector development of biotechnologies that harness the metabolic problem-solving power of microbial communities. In this context, recovery has emerged as an organizing principal to create value from industrial and municipal waste streams, and the search is on for new enzymes and platforms that can be used for waste resource recovery at scale. Enzyme surface display on cells or functionalized materials has emerged as a promising platform for waste valorization. Typically, surface display involves the use of substrate binding or catalytic domains of interest translationally fused with extracellular membrane proteins in a microbial chassis. Novel display systems with improved performance features include S-layer display with increased protein density, spore display with increased resistance to harsh conditions, and intracellular inclusions including DNA-free cells or nanoparticles with improved social licence for in situ applications. Combining these display systems with advances in bioprinting, electrospinning and high-throughput functional screening have potential to transform outmoded extractive paradigms into 'trans-metabolic" processes for remediation and waste resource recovery within an emerging circular bioeconomy.

A versatile tag for simple preparation of cutinase towards enhanced biodegradation of polyethylene terephthalate

Enzymatic degradation of polyethylene terephthalate (PET) suffered from challenges such as complex and costly enzyme preparation, difficult access to PET substrates, poor reusability of free enzymes and sometimes MHET inhibitions. Herein, we propose an "all-in-one" strategy to address these issues with a well-designed elastin-like polypeptides (ELPs) tag. The preparation of the ELPs-tagged cutinase (ET-C) was efficient and easy to scale up by centrifugation, with an activity recovery of 57.55 % and a yield of 160 mg/L. Besides, the activity of the ET-C was 1.3 and 1.66-fold higher in degrading PET micro- and macro-plastics compared to wild-type cutinase. The self-immobilized cutinase (ET-C@SiO₂) obtained by the ELPs-mediated biosilicification exhibited high loading capacity, activity, and thermostability and maintained 77.65 % of the original activity after 10 reuses. Interestingly, the product of the ET-C was TPA, whereas the wild-type was TPA and MHET. This is a simple way to release the intermediates inhibition compared with the existing methods. Our results demonstrated the feasibility of the versatile ELPs tag, which will pave an alternative economic way for scalable PET biodegradation.

Immobilized enzyme/microorganism complexes for degradation of microplastics: A review of recent advances, feasibility and future prospects

Environmental prevalence of microplastics has prompted the development of novel methods for their removal, one of which involves immobilization of microplastics-degrading enzymes. Various materials including nanomaterials have been studied for this purpose but there is currently a lack of review to present these studies in an organized manner to highlight the advances and feasibility. This article reviewed more than 100 peer-reviewed scholarly papers to elucidate the latest advances in the novel application of immobilized enzyme/microorganism complexes for microplastics degradation, its feasibility and future prospects. This review shows that metal nanoparticle-enzyme complexes improve biodegradation of microplastics in most studies through creating photogenerated radicals to facilitate polymer oxidation, accelerating growth of bacterial consortia for biodegradation, anchoring enzymes and improving their stability, and absorbing water for hydrolysis. In a study, the antimicrobial property of nanoparticles retarded the growth of microorganisms, hence biodegradation. Carbon particle-enzyme complexes enable enzymes to be immobilized on carbon-based support or matrix through covalent bonding, adsorption, entrapment, encapsulation, and a combination of the mechanisms, facilitated by formation of cross-links between enzymes. These complexes were shown to improve microplastics-degrading efficiency and recyclability of enzymes. Other emerging nanoparticles and/or enzymatic technologies are fusion of enzymes with hydrophobins, polymer binding module, peptide and novel nanoparticles. Nonetheless, the enzymes in the complexes present a limiting factor due to limited understanding of the degradation mechanisms. Besides, there is a lack of studies on the degradation of polypropylene and polyvinyl chloride. Genetic bioengineering and metagenomics could provide breakthrough in this area. This review highlights the optimism of using immobilized enzymes/microorganisms to increase the efficiency of microplastics degradation but optimization of enzymatic or microbial activities and synthesis of immobilized enzymes/microorganisms are crucial to overcome the barriers to their wide application.

Cell population behavior of the unicellular red alga Galdieria sulphuraria during precious metal biosorption

This study investigates the biosorption mechanism, including cell population behavior, of trace amounts of precious metals (gold, palladium, and platinum) in a unicellular red alga, Galdieria sulphuraria. Single-cell inductively coupled plasma mass spectrometry showed that the number of adsorbing cells and the concentration of adsorbed metal per cell varied depending on solution acidity and metal species. The X-ray absorption fine structure in 5 mM HCl solution indicated that the adsorbed Au formed inner-sphere complexes with S, whereas the adsorbed Pd and Pt formed an inner-sphere complexes with N and/or S. In 500 mM HCl solution, the adsorbed Au and Pd formed inner-sphere complexes only with S, and the Au formed a structure similar to Au₂S. At higher acidity, Au and Pd were recovered by interacting with residues that formed more stable complexes, which was accompanied by changes in the behavior of cell populations adsorbing the metals. This is the first study to demonstrate the relationship between changes in the behavior of cell populations and chemical interactions that occur between substrate elements and biomaterial residues during biosorption. The findings of this study provide deeper insights into the biosorption mechanism and a background for the design of an environmentally friendly biosorbent.

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.

Recovery of Au from dilute aqua regia solutions via adsorption on the lyophilized cells of a unicellular red alga Galdieria sulphuraria: A mechanism study

The high electrical conductivity, chemical stability, and low toxicity of elemental Au make it a highly valuable resource. However, wastewater produced during the mining, utilization, and disposal of Au inevitably contains small amounts (10-40 mg L^-1) of Au, thus posing environmental risks. It is too acidic to be treated with inexpensive and eco-friendly bioadsorbents previously studied for the remediation of less acidic effluents. Herein, lyophilized Galdieria sulphuraria cells are shown to directly adsorb Au from simulated Au-containing wastewater with a total acid concentration of 4 M, achieving an adsorption capacity of 35 ± 2.5 mg g^-1 Au after 30-min exposure and a selectivity that exceeds that of an ion-exchange resin and is comparable to that of activated carbon. Additionally, Au adsorbed on these cells is more easily eluted than that adsorbed on the ion-exchange resin or activated carbon. Detailed characterizations reveal that Au accumulates on the surface of lyophilized cells, where it is mainly present as AuCl₄^- and not as Au⁰, in contrast to a previously proposed adsorption mechanism. Thus, our work provides valuable insights into the mechanism of Au adsorption on biomaterials and paves the way to the cheap and eco-friendly recovery of Au from acidic wastewater.

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.

Making Waves: Biocatalysis and Biosorption: Opportunities and Challenges Associated with a New Protein-Based Toolbox for Water and Wastewater Treatment

New water and wastewater treatment technologies are required to meet the demands created by emerging contaminants and resource recovery needs, yet technology development is a slow and uncertain process. Through evolution, nature has developed highly selective and fast-acting proteins that could help address these issues, but research and application have been limited, often due to assumptions about stability and economic feasibility. Here we highlight the potential advantages of cell-free, protein-based water and wastewater treatment processes (biocatalysis and biosorption), evaluate existing information about their economic feasibility, consider when a protein-based treatment process might be advantageous, and highlight key research needs.

Risk Perception and Coping Behavior of Construction Workers on Occupational Health Risks-A Case Study of Nanjing, China

To reduce harm caused by occupational health risks of construction workers exposed to working environments, especially those for interior decoration, it is crucial for them to actively recognize and prevent these risks. Therefore, how to improve their occupational health risks perception and regulate their coping behaviors should be of great concern. However, most prior studies target construction worker safety, and little research focuses on risk analysis from the psychological level of workers. Hence, construction workers' occupational health risk perception level and coping behavior level in Nanjing and the influencing factors were analyzed through statistical analysis with 341 valid questionnaires. Bootstrapping was applied to test the mediating effects of risk perception on the proposed factors and coping behaviors. This study revealed that construction workers have a high-level of occupational health risk perception, yet low-level coping behavior. Gender, age, education level, and unit qualification cause differences in individual risk perception level. Personal knowledge and group effects significantly affect the level of risk perception, which subsequently affect coping behavior. Education level, monthly income, and personal knowledge influence the coping behavior through risk perception. Recommendations were put forward for risk perception and coping behavior improvement from the perspectives of construction workers themselves, enterprises, and governments. This study sheds new light for research areas of occupational health and risk management and provides beneficial practice for improving construction workers' responses to occupational health risks.

Biodegradation of aromatic pollutants meets synthetic biology

Ubiquitously distributed microorganisms are natural decomposers of environmental pollutants. However, because of continuous generation of novel recalcitrant pollutants due to human activities, it is difficult, if not impossible, for microbes to acquire novel degradation mechanisms through natural evolution. Synthetic biology provides tools to engineer, transform or even re-synthesize an organism purposefully, accelerating transition from unable to able, inefficient to efficient degradation of given pollutants, and therefore, providing new solutions for environmental bioremediation. In this review, we described the pipeline to build chassis cells for the treatment of aromatic pollutants, and presented a proposal to design microbes with emphasis on the strategies applied to modify the target organism at different level. Finally, we discussed challenges and opportunities for future research in this field.

Enzyme Discovery and Engineering for Sustainable Plastic Recycling

The drastically increasing amount of plastic waste is causing an environmental crisis that requires innovative technologies for recycling post-consumer plastics to achieve waste valorization while meeting environmental quality goals. Biocatalytic depolymerization mediated by enzymes has emerged as an efficient and sustainable alternative for plastic treatment and recycling. A variety of plastic-degrading enzymes have been discovered from microbial sources. Meanwhile, protein engineering has been exploited to modify and optimize plastic-degrading enzymes. This review highlights the recent trends and up-to-date advances in mining novel plastic-degrading enzymes through state-of-the-art omics-based techniques and improving the enzyme catalytic efficiency and stability via various protein engineering strategies. Future research prospects and challenges are also discussed.

A selected bacterial strain for the self-healing process in cementitious specimens without cell immobilization steps

The use of microorganisms capable of mediating the bioprecipitation process can be an important application in the self-healing processes of cement specimens. Thus, the present study identified and evaluated five Bacillus strains for potential application in the protocol of self-healing via bioprecipitation. Cell growth, enzyme production, and kinetic parameters conditions were evaluated during the fermentation process. Based on the analysis of 16S rDNA in conjunction with biochemical testing, results demonstrate that the strains are either Bacillus cereus or Bacillus thuringiensis. Strategically it was found that the addition of glycerol to fermentative medium was essential to increase the bacterial concentration (≈ 4.2 × 10⁷ cells mL^-1) and production of the enzyme urease (≈ 3.623,2 U.mL^-1). The addition of this medium after 40 days of fermentation promoted the self-healing of cracks and increased compressive strength in ≈ 14.2% of the cementitious specimens; therefore, increasing the sustainability and engineering properties of cement-based materials.