Bioremediation potential of Cd by transgenic yeast expressing a metallothionein gene from Populus trichocarpa

Heavy metal mitigation in soil and plants using organic and inorganic amendments alone and in combination

The use of organic and inorganic amendments like stilbite-zeolite (SZ) and nano-biochar (NBC) in phytoremediation holds immense promise, long-term stability, and its effectiveness necessitate comprehensive research. This study aimed to evaluate their potential in mitigating heavy metal contamination in soil and plants. Our results shows that SZ and NBC treatments significantly impacted heavy metal levels, notably reducing arsenic (As), nickel (Ni), lead (Pb), cadmium (Cd), and mercury (Hg) accumulation in plant tissues. The treatments exhibited varying degrees of effectiveness in reducing heavy metal levels. Notably, SZ2 treatment decreased As and Pb levels by 33.33% and 20%, respectively, while NBC3 achieved even greater reductions, lowering As by 53.33% and Pb by 30%. Moreover, SZ2, SZ5, and NBC3 treatments halved Cd levels, showcasing their potential in mitigating heavy metal contamination in rice. However Hg levels remained largely unaffected, except for NBC1, which unexpectedly doubled its concentration. In soil, SZ2 treatment significantly reduced metal concentrations, particularly Cd (66.8% reduction) and Hg (70.7% reduction). Conversely, SZ3 and SZ7 treatments increased metal concentrations, suggesting that certain zeolite applications might enhance metal bioavailability. NBC treatments showed varying effectiveness, with NBC3 being the most effective, substantially reducing As, Pb, and Cd levels.

Microbe-assisted phytoremediation for sustainable management of heavy metal in wastewater - A green approach to escalate the remediation of heavy metals

Water pollution from Heavy metal (HM) contamination poses a critical threat to environmental sustainability and public health. Industrial activities have increased the presence of HMs in wastewater, necessitating effective remediation strategies. Conventional methods like chemical precipitation, ion exchange, adsorption, and membrane filtration are widely used but possess various limitations. These include high costs, environmental impacts, and the potential for generating secondary pollutants, highlighting the need for sustainable alternatives. Phytoremediation, enhanced by microbial interactions, offers an eco-friendly solution to this issue. The unique physiological and biochemical traits of plants, combined with microbial metabolic capabilities, enable efficient uptake and detoxification of HMs. Microbial enzymes play a crucial role in these processes by breaking down complex compounds, enhancing HM bioavailability, and facilitating their conversion into less toxic forms. Synergistic interactions between root-associated microbes and plants further improves metal absorption and stabilization, boosting phytoremediation efficiency. However, challenges remain, including the limited bioavailability of contaminants and plant resilience in highly polluted environments. Recent advancements focus on improving microbial-assisted phytoremediation through mechanisms like bioavailability facilitation, phytoextraction, and phytostabilization. Genetic engineering facilitates the altering of genes that control plant immune responses and growth which improves the ability of plants to interact beneficially with microbes to thrive in HM rich environments while efficiently cleaning contaminated wastewater. This review examines these strategies and highlights future research directions to enhance wastewater remediation using phytoremediation technologies.

Metallothionein family genes in kiwifruit: characterization and determining their roles in plant's response to different stresses

Kiwifruit growth and development are severely affected by various biotic and abiotic stresses, especially cold stress and the bacterial disease caused by Pseudomonas syringae pv. actinidiae (Psa). Metallothioneins (MTs) are a group of cysteine-rich proteins that play crucial roles in stress response, metal detoxification, and homeostasis in plants. However, the protective role of these MTs in kiwifruit remains to be elucidated. In the present study, four AcMT genes were identified in the Hongyang kiwifruit genome, namely, two Type 2 isoforms (AcMT2 and AcMT2a) and two Type 3 isoforms (AcMT3a and AcMT3b) located separately on four different chromosomes. The hormones and stress response cis-elements within the promoter regions of these AcMTs were characterized. It was revealed that the four AcMT genes exhibited different expression patterns in different tissues: AcMT2 and AcMT2a were expressed at much higher levels in the fruit, male flower, female flower, root, and bark, while AcMT3a was expressed mainly in the fruit and AcMT3b was expressed highly in the bark. The expression patterns of these AcMT genes after exposure to Psa infection and different phytohormones, including gibberellic acid A3(GA3), ethylene (ET), and abscisic acid (ABA), were evaluated. It was revealed that in response to Psa infection, the main AcMTs in each tissue (those with expression levels higher compared to the other MTs in that tissue) were downregulated during the early stage in kiwifruits, followed by a recovery phase. In addition, most AcMTs were downregulated after exposure to ET and GA3, while type 2 AcMTs (AcMT2 and AcMT2a) were upregulated after treatment with ABA. The overexpression of AcMTs in Escherichia coli presented a higher tolerance to H2O2, heavy metals, low temperature, and high temperature. Collectively, these findings demonstrated the protective roles of AcMTs in terms of stress resistance conferred through plant hormone-related signal pathways.

Metallothionein: A Comprehensive Review of Its Classification, Structure, Biological Functions, and Applications

Metallothionein is a cysteine-rich protein with a high metal content that is widely found in nature. In addition to heavy metal detoxification, metallothionein is well known as a potent antioxidant. The high sulfhydryl content of metallothionein confers excellent antioxidant activity, enabling it to effectively scavenge free radicals and mitigate oxidative stress damage. In addition, metallothionein can play a neuroprotective role by alleviating oxidative damage in nerve cells, have an anticancer effect by enhancing the ability of normal cells to resist unfavorable conditions through its antioxidant function, and reduce inflammation by scavenging reactive oxygen species. Due to its diverse biological functions, metallothionein has a broad potential for application in alleviating environmental heavy metal pollution, predicting and diagnosing diseases, and developing skin care products and health foods. This review summarizes the recent advances in the classification, structure, biological functions, and applications of metallothionein, focusing on its powerful antioxidant effects and related functions.

Mitigation strategies for heavy metal toxicity and its negative effects on soil and plants

Heavy metal pollution threatens food security by accumulating in crops and soils, posing a significant challenge to modern agriculture due to its high toxicity. Urgent action is needed to restore affected agricultural fields. An efficient way to remove toxins is by bioremediation, which uses microorganisms. With the purpose of restoring soil in agriculture, this research attempts to assemble a consortium of microorganisms isolated from techno-genic soil. A number of promising strains, including Pseudomonas putida, Pantoea sp., Pseudomonas aeruginosa, Klebsiella oxytoca, and Agrobacterium tumefaciens were chosen based on their capacity to eliminate heavy metals from tests. Heavy metal removal (Cd, Hg, As, Pb, and Ni) and phytohormone production have been shown to be effective using consortiums (Pseudomonas aeruginosa, Klebsiella oxytoca, and Agrobacterium tumefaciens in a 1:1:2). In instances with mixed heavy-metal contamination, aeruginosa demonstrated efficacy because of its notable ability to absorb substantial quantities of heavy metals. The capacity of the cooperation to improve phytoremediation was investigated, with an emphasis on soil cleanup in agricultural areas. When combined with Sorghum bicolor L., it was able to remove roughly 16% As, 14% Hg, 32% Ni, 26% Cd, and 33% Pb from the soil.

Functional characterization of rice metallothionein OsMT-I-Id: Insights into metal binding and heavy metal tolerance mechanisms

Metallothioneins (MTs) are cysteine-rich proteins known for their strong metal-binding capabilities, making them effective in detoxifying heavy metals (HMs). This study focuses on characterizing the functional properties of OsMT-I-Id, a type-I Metallothionein found in rice. Using a HM-responsive yeast cup1Δ (DTY4), ycf1∆ (for cadmium), and acr3∆ mutants (for trivalent arsenic), we assessed the impact of OsMT-I-Id on metal accumulation and cellular resilience. Our results demonstrated that yeast cells expressing OsMT-I-Id showed increased tolerance and accumulated higher levels of copper (Cu), arsenic (As), and cadmium (Cd), compared to control cells. This can be attributed to the protein's ability to chelate and bind HMs. Site-directed mutagenesis was employed to investigate the specific contributions of cysteine residues. The study revealed that yeast cells with a mutated C-domain displayed heightened HM sensitivity, while cells with a mutated N-domain exhibited reduced sensitivity. This underscores the critical role of C-cysteine-rich domains in metal binding and tolerance of type-I rice MTs. Furthermore, the study identified the significance of the 12th cysteine position at the N-domain and the 68th and 72nd cysteine positions at the C-domain in influencing OsMT-I-Id metal-binding capacity. This research provides novel insights into the structure-function relationship and metal binding properties of type-I plant MTs.

Microorganisms for Bioremediation of Soils Contaminated with Heavy Metals

Heavy-metal contaminants are one of the most relevant problems of contemporary agriculture. High toxicity and the ability to accumulate in soils and crops pose a serious threat to food security. To solve this problem, it is necessary to accelerate the pace of restoration of disturbed agricultural lands. Bioremediation is an effective treatment for agricultural soil pollution. It relies on the ability of microorganisms to remove pollutants. The purpose of this study is to create a consortium based on microorganisms isolated from technogenic sites for further development in the field of soil restoration in agriculture. In the study, promising strains that can remove heavy metals from experimental media were selected: Pantoea sp., Achromobacter denitrificans, Klebsiella oxytoca, Rhizobium radiobacter, and Pseudomonas fluorescens. On their basis, consortiums were compiled, which were investigated for the ability to remove heavy metals from nutrient media, as well as to produce phytohormones. The most effective was Consortium D, which included Achromobacter denitrificans, Klebsiella oxytoca, and Rhizobium radiobacter in a ratio of 1:1:2, respectively. The ability of this consortium to produce indole-3-acetic acid and indole-3-butyric acid was 18.03 μg/L and 2.02 μg/L, respectively; the absorption capacity for heavy metals from the experimental media was Cd (56.39 mg/L), Hg (58.03 mg/L), As (61.17 mg/L), Pb (91.13 mg/L), and Ni (98.22 mg/L). Consortium D has also been found to be effective in conditions of mixed heavy-metal contamination. Due to the fact that the further use of the consortium will be focused on the soil of agricultural land cleanup, its ability to intensify the process of phytoremediation has been studied. The combined use of Trifolium pratense L. and the developed consortium ensured the removal of about 32% Pb, 15% As, 13% Hg, 31% Ni, and 25% Cd from the soil. Further research will be aimed at developing a biological product to improve the efficiency of remediation of lands withdrawn from agricultural use.

Fungal bioproducts for petroleum hydrocarbons and toxic metals remediation: recent advances and emerging technologies

Petroleum hydrocarbons and toxic metals are sources of environmental contamination and are harmful to all ecosystems. Fungi have metabolic and morphological plasticity that turn them into potential prototypes for technological development in biological remediation of these contaminants due to their ability to interact with a specific contaminant and/or produced metabolites. Although fungal bioinoculants producing enzymes, biosurfactants, polymers, pigments and organic acids have potential to be protagonists in mycoremediation of hydrocarbons and toxic metals, they can still be only adjuvants together with bacteria, microalgae, plants or animals in such processes. However, the sudden accelerated development of emerging technologies related to the use of potential fungal bioproducts such as bioinoculants, enzymes and biosurfactants in the remediation of these contaminants, has boosted fungal bioprocesses to achieve higher performance and possible real application. In this review, we explore scientific and technological advances in bioprocesses related to the production and/or application of these potential fungal bioproducts when used in remediation of hydrocarbons and toxic metals from an integral perspective of biotechnological process development. In turn, it sheds light to overcome existing technological limitations or enable new experimental designs in the remediation of these and other emerging contaminants.

Heterologous expression of the tobacco metallothionein gene NtMT2F confers enhanced tolerance to Cd stress in Escherichia coli and Arabidopsis thaliana

Heavy metal pollution in the soil is a serious threat to crop growth and human health. Metallothionein (MT) is a low molecular weight protein that is rich in cysteine, which can effectively alleviate the toxicity of heavy metals in plants. In this study, a novel metallothionein encoding gene, NtMT2F, was cloned from the Cd-hyperaccumulator tobacco and heterologously expressed in E. coli and A. thaliana to verify its biological function. Recombinant E. coli incubated with NtMT2F effectively resisted heavy metal stress, particularly Cd. The recombinant strain grew significantly faster and had a higher content of Cd than the control. Mutations in the C-terminal Cys residues of NtMT2F significantly reduced its ability to chelate heavy metals. The overexpression of NtMT2F significantly enhanced resistance to Cd toxicity in transgenic A. thaliana. The germination rate, root length, and fresh weight of transgenic plants under Cd stress were higher than those of the wild type (WT). The contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) were lower than those of the WT. In addition, the activities of anti-peroxidase enzymes including glutathione reductase (GR), catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), were significantly increased in the transgenic plants. The results of this study indicate that NtMT2F significantly improved the tolerance of microorganisms and plants to Cd and could be an important candidate protein for phytoremediation.

Engineered microbes as effective tools for the remediation of polyaromatic aromatic hydrocarbons and heavy metals

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) have become a major concern to human health and the environment due to rapid industrialization and urbanization. Traditional treatment measures for removing toxic substances from the environment have largely failed, and thus development and advancement in newer remediation techniques are of utmost importance. Rising environmental pollution with HMs and PAHs prompted the research on microbes and the development of genetically engineered microbes (GEMs) for reducing pollution via the bioremediation process. The enzymes produced from a variety of microbes can effectively treat a range of pollutants, but evolutionary trends revealed that various emerging pollutants are resistant to microbial or enzymatic degradation. Naturally, existing microbes can be engineered using various techniques including, gene engineering, directed evolution, protein engineering, media engineering, strain engineering, cell wall modifications, rationale hybrid design, and encapsulation or immobilization process. The immobilization of microbes and enzymes using a variety of nanomaterials, membranes, and supports with high specificity toward the emerging pollutants is also an effective strategy to capture and treat the pollutants. The current review focuses on successful bioremediation techniques and approaches that make use of GEMs or engineered enzymes. Such engineered microbes are more potent than natural strains and have greater degradative capacities, as well as rapid adaptation to various pollutants as substrates or co-metabolizers. The future for the implementation of genetic engineering to produce such organisms for the benefit of the environment andpublic health is indeed long and valuable.

Research on safety and compliance of imported microbial inoculants using high-throughput sequencing

Microbial inoculants are widely used in wastewater treatment, soil remediation, and biological control. Safety and compliance for active constituents are considered to be the most important measures of imported microbial inoculants. Microbial inoculants composition was commonly identified by phenotypic culture, which is time-consuming and labor intense with occasionally false negative results provided, and can only be tested for specific species. High-throughput sequencing (HTS), known for its non-targeted detection of unknown species composition in samples, is suitable for composition consistency identification and biosafety analysis of imported microbial inoculants. In this study, the application of HTS for microflora distribution and resistance gene was verified in microbial inoculants for environmental protection and then applicated in imported microbial inoculants. Both Illumina- and Nanopore-based HTS methods identified the same dominant bacterial species successfully in the imported microbial inoculants. The main component of bacterial species was Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus licheniformis, and Enterococcus faecium, and further confirmed with traditional methods. The antibiotic resistance genes Bacillus subtilis mprF, bcrA, blt, lmrB, rphB, tet(L), tmrB, vmlR, ykkC, and ykkD were detected in all samples. Our results indicated that HTS processes the application potential to identify the active ingredients of microbial inoculants. Therefore, rapid and accurate identification of the microbial compositions in microbial formulation products is of high importance for port biosafety supervision.

Engineered bacterium-binding protein promotes root recruitment of functional bacteria for enhanced cadmium removal from wastewater by phytoremediation

Functional bacteria promote the efficiency of phytoremediation by enhancing plant growth and participating in decontamination. However, their activity is frequently compromised by the weakness of their interaction with plant roots. In this study, we designed the artificial protein LcGC composed of a bacterium-binding domain, a GFP fluorescence reporter, and a carbohydrate-binding domain to function as a physical contact between functional bacteria and plant roots. This protein was then expressed in an engineered yeast cell factory and extracted to assess its effect on rhizosphere microbiome composition, plant growth, and cadmium removal in a simulated phytoremediation system containing the remediation plant Lemna minor and the functional heavy metal-capturing bacteria Cupriavidus taiwanensis and Pseudomonas putida. LcGC efficiently bound bacterial cell wall components and glucan, endowing it high efficiency to bind both functional bacteria and plant roots. Scanning microscopy and microbiome analysis revealed that LcGC enhanced root recruitment and colonization of functional bacteria on the root surfaces. Furthermore, LcGC with the aid of single C. taiwanensis or of C. taiwanensis and P. putida in combination promoted plant growth, enhanced tolerance to cadmium-induced oxidative stress, and consequently improved cadmium-removing capacity of the plants, with the percent of cadmium removal reaching up to 91% for LcGC plus C. taiwanensis, and to 96% for LcGC plus C. taiwanensis and P. putida on day 7. This study provided a physical contact-based strategy to enhance the interaction between functional microbes and plant roots for efficient phytoremediation.

Genetically modified metallothionein/cellulose composite material as an efficient and environmentally friendly biosorbent for Cd2+ removal

Metallothioneins (MTs) are a class of cysteine-rich metal-binding proteins. Cadmium (Cd) is one of the toxic heavy metal pollutants. In our previous research, the full-length cDNA of MT (Cd specificity) from freshwater crab (Sinopotamon henanense) (ShMT) was cloned and genetically modified to ShMT3 by site-directed mutagenesis to enhance the tolerance for Cd²⁺, however, it was limited in actual Cd²⁺ adsorption due to instability. Here, ShMT3-CBM, a novel recombinant fusion protein, was prepared. CBM is a carbohydrate binding module that can specifically bind cellulose while ShMT3 can effectively chelate Cd²⁺. The biosorbent Cellulose1-ShMT3-CBM was obtained by screening suitable cellulose materials. The selective adsorption experiments showed that Cellulose1-ShMT3-CBM had a preference for Cd²⁺. In low-concentration Cd²⁺ solutions, the removal efficiency was >99 %, and the adsorption equilibrium was reached within 15 min. The saturated adsorption capacity of Cellulose1-ShMT3-CBM for Cd²⁺ is 180.35 ± 4.67 mg/g (Dry Weight). Regeneration experiments showed that adsorption efficiency was maintained after six cycles. The MTT experiment showed that Cellulose1-ShMT3-CBM had low cytotoxicity. Meanwhile, Cellulose1-ShMT3-CBM can preferentially remove Cd²⁺ in actual water samples and boiler sewage. In this study, an environmentally friendly biosorbent which can adsorb Cd²⁺ efficiently and quickly was prepared for actual water treatment.

Yeast Genomics and Its Applications in Biotechnological Processes: What Is Our Present and Near Future?

Since molecular biology and advanced genetic techniques have become important tools in a variety of fields of interest, including taxonomy, identification, classification, possible production of substances and proteins, applications in pharmacology, medicine, and the food industry, there has been significant progress in studying the yeast genome and its potential applications. Because of this potential, as well as their manageability, safety, ease of cultivation, and reproduction, yeasts are now being extensively researched in order to evaluate a growing number of natural and sustainable applications to provide many benefits to humans. This review will describe what yeasts are, how they are classified, and attempt to provide a rapid overview of the many current and future applications of yeasts. The review will then discuss how yeasts—including those molecularly modified—are used to produce biofuels, proteins such as insulin, vaccines, probiotics, beverage preparations, and food additives and how yeasts could be used in environmental bioremediation and biocontrol for plant infections. This review does not delve into the issues raised during studies and research, but rather presents the positive outcomes that have enabled several industrial, clinical, and agricultural applications in the past and future, including the most recent on cow-free milk.

Roles of Canavalia rosea metallothioneins in metal tolerance and extreme environmental adaptation to tropical coral reefs

Canavalia rosea (Sw.) DC is a perennial twining herb distributed in the semi-arid and saline-alkali areas of coastal regions and has evolved halotolerance. In this study, we present the first comprehensive survey of the metallothionein (MT) gene family in C. rosea. MT proteins belong to a family of low-molecular-weight polypeptides with a high content of cysteine residues, which have an affinity to bind with heavy metal ions. MTs also play important roles in stress responses as reactive oxygen species (ROS) scavengers. A total of six CrMTs were identified in the C. rosea genome and classified into four subgroups by phylogenetic analysis. An analysis of the cis-acting elements revealed that a series of hormone-, stress-, and development-related cis-acting elements were present in the promoter regions of CrMTs. The expression of CrMTs also showed habitat- and environmental stress-regulated patterns in C. rosea. CrMT overexpression in yeast enhanced tolerance to heavy metals and ROS, as well as high osmotic and alkalinity stress, which is consistent with their predicted roles as metal-chelating proteins and ROS scavengers. Our results indicate that the CrMT genes might contribute to the detoxification of plants to metals and provide marked tolerance against abiotic stress. The expression patterns of CrMTs in C. rosea also indicate that CrMTs play important roles in this species' response to extreme environments on tropical islands and reefs, probably by improving the thermotolerance of C. rosea plants.

Novel Latex Microsphere Immunochromatographic Assay for Rapid Detection of Cadmium Ion in Asparagus

Recently, concerns about heavy metal cadmium ion (Cd²⁺) residue in asparagus have been frequently reported, and there is an urgent need to develop an effective, sensitive, and rapid detection method for Cd²⁺. In this study, we innovatively combined molecular microbiology to carry out the comparative screening of Cd²⁺ chelators in a green, efficient, and specific way. The knock-out putative copper-transporter gene (pca1Δ) yeast strain with high sensitivity to Cd²⁺ was first used to screen the Cd²⁺ chelator, and the optimum chelator 1-(4-Isothiocyanatobenzyl)ethylenediamine-N,N,N,N′-tetraacetic acid (ITCBE) was obtained. Additionally, a rapid latex microsphere immunochromatographic assay (LMIA) was developed, based on the obtained monoclonal antibody (mAb) with high specificity and high affinity (affinity constant Ka = 1.83 × 10¹⁰ L/mol), to detect Cd²⁺ in asparagus. The 50% inhibitive concentration (IC₅₀) of test strip was measured to be 0.2 ng/mL, and the limit of detection (IC₁₀) for qualitative (LOD, for visual observation) and quantitative detection (LOQ, for data simulation) of the test strip was 2 ng/mL and 0.054 ng/mL, respectively. In all, the developed mAb-based LMIA shows a great potential for monitoring Cd²⁺ in asparagus, even in vegetable samples.

Genetically engineered microbial remediation of soils co-contaminated by heavy metals and polycyclic aromatic hydrocarbons: Advances and ecological risk assessment

Soils contaminated with heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) have been becoming a worldwide concerned environmental problem because of threatening public healthy via food chain exposure. Thus soils polluted by HMs and PAHs need to be remediated urgently. Physical and chemical remediation methods usually have some disadvantages, e.g., cost-expensiveness and incomplete removal, easily causing secondary pollution, which are hence not environmental-friendly. Conventional microbial approaches are mostly used to treat a single contaminant in soils and lack high efficiency and specificity for combined contaminants. Genetically engineered microorganisms (GEMs) have emerged as a desired requirement of higher bioremediation efficiency for soils polluted with HMs and PAHs and environmental sustainability, which can provide a more eco-friendly and cost-effective strategy in comparison with some conventional techniques. This review comments the recent advances about successful bioremediation techniques and approaches for soil contaminated with HMs and/or PAHs by GEMs, and discusses some challenges in the simultaneous removal of HMs and PAHs from soil by designing multi-functional genetic engineering microorganisms (MFGEMs), such as improvement of higher efficiency, strict environmental conditions, and possible ecological risks. Also, the modern biotechnological techniques and approaches in improving the ability of microbial enzymes to effectively degrade combined contaminants at a faster rate are introduced, such as reasonable gene editing, metabolic pathway modification, and protoplast fusion. Although MFGEMs are more potent than the native microbes and can quickly adapt to combined contaminants in soils, the ecological risk of MFGEMs needs to be evaluated under a regulatory, safety, or costs benefit-driving system in a way of stratified regulation. Nevertheless, the innovation of genetic engineering to produce MFGEMs should be inspired for the welfare of successful bioremediation for soils contaminated with HMs and PAHs but it must be supervised by the public, authorities, and laws.

Genetic modifications of metallothionein enhance the tolerance and bioaccumulation of heavy metals in Escherichia coli

Metallothioneins (MTs) are low molecular weight cysteine-rich proteins that bind to metals. Owing to their high cysteine (Cys) content, MTs are effective mediators of heavy metal detoxification. To enhance the heavy metal binding ability of MT from the freshwater crab Sinopotamon henanense (ShMT), sequence-based multiple sequence alignment (MSA) and structure-based molecular docking simulation (MDS) were conducted in order to identify amino acid residues that could be mutated to bolster such metal-binding activity. Site-directed mutagenesis was then used to modify the primary structure of ShMT, and the recombinant proteins were further enhanced using the SUMO fusion expression system to yield SUMO-ShMT1, SUMO-ShMT2, and SUMO-ShMT3 harboring one-, two-, and three- point mutations, respectively. The resultant modified proteins were primarily expressed in a soluble form and exhibited the ability to readily bind to heavy metals. Importantly, these modified proteins exhibited significantly enhanced heavy metal binding capacities, and they improved Cd²⁺, Cu²⁺ and Zn²⁺ tolerance and bioaccumulation in Escherichia coli (E. coli) in a manner dependent upon the number of introduced point mutations (SUMO-ShMT3 > SUMO-ShMT2 > SUMO-ShMT1 > SUMO-ShMT > control). Indeed, E. coli cells harboring the pET28a-SUMO-ShMT3 expression vector exhibited maximal Cd²⁺, Cu²⁺, and Zn²⁺ bioaccumulation that was increased by 1.86 ± 0.02-, 1.71 ± 0.03-, and 2.13 ± 0.02-fold relative to that in E. coli harboring the pET28a-SUMO-ShMT vector. The present study offers a basis for the preparation of genetically engineered bacteria that are better able to bioaccumulate and tolerate heavy metals, thus providing a foundation for biological heavy metal water pollution treatment.

Biosorption: A Review of the Latest Advances

Biosorption is a variant of sorption techniques in which the sorbent is a material of biological origin. This technique is considered to be low cost and environmentally friendly, and it can be used to remove pollutants from aqueous solutions. The objective of this review is to report on the most significant recent works and most recent advances that have occurred in the last couple of years (2019–2020) in the field of biosorption. Biosorption of metals and organic compounds (dyes, antibiotics and other emerging contaminants) is considered in this review. In addition, the use and possibilities of different forms of biomass (live or dead, modified or immobilized) are also considered.