A review on remediation of cyanide containing industrial wastes using biological systems with special reference to enzymatic degradation

Expanding Yarrowia lipolytica's metabolic potential for detoxification of cyanogenic glycosides in edible plants

Cyanides are highly toxic chemicals in several edible plants that threaten food safety and human health. A phenotypically distinct Yarrowia lipolytica strain that efficiently detoxifies multiple cyanogenic glycosides from edible plants was constructed using a family 1 glycosyl-hydrolase (GH1). The strain displayed higher growth rates and metabolic activities when exposed to high concentrations of cyanides than the wild-type. It overexpressed genes that promoted the binding of molecular oxygen to the cytochrome iv complex. The engineered strain repressed fatty acid production to optimize energy production and activated the cyanide-resistant respiratory (AOX) pathway to circumvent HCN toxicity and maintain cellular homeostasis. It upregulated ribosome biogenesis, the sec-dependent protein export pathway, and the sulfur relay system to facilitate the production and transmembrane efflux of the secreted GH1 hydrolase. It efficiently degraded linamarin, amygdalin, prunasin, and dhurrin in food plants including cassava, germinated sorghum and Apricot seeds. The strain produced high phospholipids to support new membrane production and could be a cost-effective source of single-cell phospholipids. The findings demonstrate that the strain is a robust, sustainable, and potentially efficient strain that could be used for industrial bioconversion of plant materials containing glycosylated toxicants into safe foods and animal feeds.

Interfacial engineering-based colonization of biofilms on polyethylene terephthalate (PET) surfaces: Implications for whole-cell biodegradation of microplastics

Microplastic pollution has become a significant environmental issue. One of the most important sources and components of microplastics is polyester fabric - polyethylene terephthalate (PET). Because the catalytic depolymerization of PET typically requires specific conditions such as alkaline environments, specific solvents, or high temperatures, there is an urgent need for a simpler, eco-friendly solution with high degradation efficiency for managing the vast amounts of PET textile waste. In this study, Comamonas testosterone F4, which we screened and cultivated to grow using PET as the sole carbon source, was utilized as a whole-cell biocatalyst. The bioprocess was optimized through interfacial engineering, which leveraged dynamic supramolecular interactions and molecular recognition at the PET-enzyme interface. Biofilms were more effectively formed on the surfaces of PET@Span-80 and PET@TRE. Through supramolecular interactions, Span-80 and Trehalose lipids (TRE), which serve as host and guest chemicals, readily adhere to the PET surface. Compared to untreated PET fibers, PET surfaces treated with biodegradable surfactants showed increased hydrophilicity, which facilitated bacterial colonization and enhanced bacterial and enzymatic activity on PET. Furthermore, combining PET@Span-80 and a strategy for renewing bacterial cultures (RBC) resulted in a high-efficiency degradation effect over an extended degradation period. The weight loss of PET increased from 2.23 % to 5.67 % after four weeks of degradation. A more efficient method for the biodegradation of PET was proposed by our team. The developed interfacial enhancement system provides a practical approach to accelerate the degradation of PET fabric waste, thereby mitigating the substantial environmental impact of polyester textile waste.

Nitrilase GiNIT from Gibberella intermedia Efficiently Degrades Nitriles Derived from Rapeseed Meal Glucosinolate

Rapeseed meal is severely restricted in its utilization as unconventional animal feed due to anti-nutritive compounds, such as glucosinolate, that are degraded to toxic nitriles such as 3-butenenitrile and 4-pentenenitrile in animals. Few studies on nitrilases that can degrade glucosinolate-derived nitriles have been reported thus far. In the present study, a nitrilase gene GiNIT from Gibberella intermedia was over-expressed in Escherichia coli and the purified recombinant nitrilase rGiNIT showed specific activities of 134.48 U/mg and 122.16 U/mg when using 3-butenenitrile and 4-pentenenitrile as substrates at the optimal pH, 7.5, and temperature, 45 °C, which is the highest reported in the literature. The conversion of 3-butenenitrile and 4-pentenenitrile by rGiNIT reached 81.89% and 80.23% after hydrolysis for 15 min and 300 min, respectively. Site-directed mutagenesis and molecular docking analysis revealed that the catalytic ability of rGiNIT depended on the substrate binding pocket comprising 13 key amino acid residues. These results provide a potential enzyme resource for rapeseed meal detoxification and theoretical guidance for protein engineering.

Physicochemical and thermodynamic properties of purified rhodanese from A. welwitschiae LOT1 and the cyanide detoxification potential of the enzyme

Rhodanese, the primary cyanide-detoxifying enzyme, plays a crucial role in mitigating the harmful effects of cyanide present in various industrial waste materials, such as battery manufacturing effluents. The bioremediation of cyanide-contaminated environments relies on efficient detoxification mechanisms, making rhodanese a valuable enzyme for biotechnological applications. This research aimed to investigate the biochemical properties of purified rhodanese produced by Aspergillus welwitschiae LOT1, a fungal strain with promising cyanide detoxification capabilities. The purified rhodanese was obtained through fermentation, precipitation, and chromatographic separations, resulting in a homogeneous band of approximately 58 kDa with a specific activity of 374 RU/mg, 28-fold purification, and 14% recovery. The enzyme exhibited optimal cyanide detoxification at pH 7 and 60 °C, with stability observed between 30 and 50 °C and pH 8-10. All metal ions examined except for Cu2+ enhanced the cyanide-degrading ability of rhodanese. Notably, the enzyme demonstrated a high substrate preference for Na2S2O3 and followed a first-order kinetic model and free energy, ΔG of 61.3 kJ/mol, making it a promising candidate for biotechnological applications. Overall, this study provides valuable insights into the biochemical properties of rhodanese from A. welwitschiae LOT1, highlighting its potential for efficient cyanide detoxification and bioremediation.

Entrapment of Cyanase from Thermomyces lanuginosus Using Biomimetic Silica and Its Application for Cyanate Bioremediation

Cyanate, a toxic product from the chemical oxidation treatment of highly toxic cyanide, can be converted to harmless ammonia and carbon dioxide by cyanase (EC 4.2.1.104). Cyanase from Thermomyces lanuginosus was entrapped in biomimetic silica to improve stability and reusability. After entrapment, the enzyme's activity increased by two-fold, and the residual activity after 30-min of incubation at 60 °C also increased by two-fold, compared to the free enzyme. After being stored at room temperature for 28 days, the entrapped cyanase retained 79% of the initial activity, while the free form retained 61%. The immobilized cyanase was successfully applied to cyanate detoxification; the co-entrapment of carbonic anhydrase from Sulfurihydrogenibium azorense decreased the amount of bicarbonate necessary for cyanate detoxification by 50%. The cyanate degradation retained 53% of the initial value after the co-entrapped cyanate and carbonic anhydrase were reused five times.

Magnetic nanoflowers: a hybrid platform for enzyme immobilization

The use of organic-inorganic hybrid nanoflowers as a support material for enzyme immobilization has gained significant attention in recent years due to their high stability, ease of preparation, and enhanced catalytic activity. However, a major challenge in utilizing these hybrid nanoflowers for enzyme immobilization is the difficulty in handling and separating them due to their low density and high dispersion. To address this issue, magnetic nanoflowers have emerged as a promising alternative enzyme immobilization platform due to their easy separation, structural stability, and ability to enhance catalytic efficiency. This review focuses on different methods for designing magnetic nanoflowers, as well as future research directions. Additionally, it provides examples of enzymes immobilized in the form of magnetic nanoflowers and their applications in environmental remediation, biosensors, and food industries. Finally, the review discusses possible ways to improve the material for enhanced catalytic activity, structural stability, and scalability.

Anaerobic cyanides oxidation with bimetallic modulation of biological toxicity and activity for nitrite reduction

Cyanide is a typical toxic reducing agent prevailing in wastewater with a well-defined chemical mechanism, whereas its exploitation as an electron donor by microorganisms is currently understudied. Given that conventional denitrification requires additional electron donors, the cyanide and nitrogen can be eliminated simultaneously if the reducing HCN/CN- and its complexes are used as inorganic electron donors. Hence, this paper proposes anaerobic cyanides oxidation for nitrite reduction, whereby the biological toxicity and activity of cyanides are modulated by bimetallics. Performance tests illustrated that low toxicity equivalents of iron-copper composite cyanides provided higher denitrification loads with the release of cyanide ions and electrons from the complex structure by the bimetal. Both isotopic labeling and Density Functional Theory (DFT) demonstrated that CN--N supplied electrons for nitrite reduction. The superposition of chemical processes reduces the biotoxicity and enhances the biological activity of cyanides in the CN-/Fe3+/Cu2+/NO2- coexistence system, including complex detoxification of CN- by Fe3+, CN- release by Cu2+ from [Fe(CN)6]3-, and NO release by nitrite substitution of -CN groups. Cyanide is the smallest structural unit of C/N-containing compounds and serves as a probe to extend the electron-donating principle of anaerobic cyanides oxidation to more electron-donor microbial utilization.

Metabolism of toxic benzonitrile and hydroxybenzonitrile isomers via several distinct central pathway intermediates in a catabolically robust Burkholderia sp

Aromatic nitriles are of considerable environmental concern, because of their hazardous impacts on the health of both humans and wildlife. In the present study, Burkholderia sp. strain BC1 was observed to be capable of utilizing toxic benzonitrile and hydroxybenzonitrile isomers singly, as sole carbon and energy sources. The results of chromatographic and spectrometric analyses in combination with oxygen uptake and enzyme activity studies, revealed the metabolism of benzonitrile as well as 2-, 3-, and 4-hydroxybenzonitriles by nitrile hydratase-amidase to the corresponding carboxylates. These carboxylates were further metabolized via central pathways, namely benzoate-catechol, salicylate-catechol, 3-hydroxybenzoate-gentisate and 4-hydroxybenzoate-protocatechute pathways in strain BC1, ultimately leading to the TCA cycle intermediates. Studies also evaluated substrate specificity profiles of both nitrile hydratase and amidase(s) involved in the denitrification of the nitriles. In addition, a few metabolic crosstalk events due to the induction of multiple operons by central metabolites were appraised in strain BC1. The present study illustrates the broad degradative potential of strain BC1, harboring diverse catabolic machinery of biotechnological importance, elucidating pathways for the assimilation of benzonitrile and that of hydroxybenzonitrile isomers for the first time.

Cloning and heterologous expression of Fusarium oxysporum nitrilase gene in Escherichia coli and evaluation in cyanide degradation

Cyanide is widely utilized in the extraction of precious metal extraction even though it has been deemed as the most toxic compound. Fusarium oxysporum has been shown to degrade cyanide through the activity of the Nitrilase enzyme. In this study, the coding sequence of nitrilase gene from F. oxysporum genomic DNA was optimized for cloning and expression in E. coli. The pUC57 containing synthetic optimized nitrilase gene was transferred into E. coli DH5α strain. This nitrilase gene was sub-cloned into pET26b (+) expression vector containing an in-built His-tag at the C-terminal end to facilitate its purification. The recombinant plasmid, pETAM1, was confirmed by PCR, digestion pattern, and sequencing. The recombinant protein was overproduced in E. coli BL21 (DE3). The results of the SDS-PAGE pattern and Western blot analysis confirmed the expression of the expected recombinant protein. For expression optimization of Nitrilase protein, M16 orthogonal experimental design of the Taguchi method was used. The effect of induction time, temperature and IPTG concentration were examined using four levels for each factors. Estimation of the amount of the expressed protein was calculated via densitometry on SDS-PAGE. The enzyme activity and expression in E. coli proved to be successful since there was ammonia production when potassium cyanide and acrylonitrile were used as substrates while the highest enzyme activity of 88% was expressed at 30 °C. The Km and Vm values of the expressed Nitrilase enzyme were determined to be 0.68 mM and 0.48 mM/min respectively.

Distribution and ecological risk assessment of priority water pollutants in surface river sediments with emphasis on industrially affected areas

Priority water pollutants comprising six plasticizers, 18 volatile organic compounds (VOCs), total petroleum hydrocarbon (TPH), 1,4-dioxane, epichlorohydrin, formaldehyde, acrylamide, and cyanides were determined in surface river sediments to assess their distribution patterns and ecological risks. Among these, di (2-ethylhexyl) phthalate (DEHP), toluene, TPH, and acrylamide were frequently found in sediments. The industrial sites had higher concentrations of ∑plasticizers (median 628 ng/g dry weight (dw)), ∑VOCs (median 3.35 ng/g dw), acrylamide (median 0.966 ng/g dw), and TPH (median 152 μg/g dw) in sediments than the mixed and non-industrial areas. The other pollutants did not show the significant differences in levels according to site types because of their relatively low detection frequencies. Volatile and soluble substances as well as hydrophobic pollutants were predominantly detected in surface sediments from industrial areas. Sediment contamination patterns were affected by the size and composition of the industrial zones around the sampling sites. The ecological risks determined using the sediment quality guidelines (DEHP, VOCs, and TPH) and the mean probable effect level quotients (DEHP) were mostly acceptable. However, the two most representative industrial regions (the largest industrial area and the first industrial city) showed risks of concern for DEHP and TPH.

The isolation of rumen enterococci strains along with high potential utilizing cyanide

Cyanogenic glycosides in forage species and the possibility of cyanide (CN) poisoning can have undesirable effects on ruminants. The literature estimates that unknown rumen bacteria with rhodanese activity are key factors in the animal detoxification of cyanogenic glycosides, as they are capable of transforming CN into the less toxic thiocyanate. Therefore, identifying these bacteria will enhance our understanding of how to improve animal health with this natural CN detoxification process. In this study, a rhodanese activity screening assay revealed 6 of 44 candidate rumen bacterial strains isolated from domestic buffalo, dairy cattle, and beef cattle, each with a different colony morphology. These strains were identified as belonging to the species Enterococcus faecium and E. gallinarum by 16S ribosomal DNA sequence analysis. A CN-thiocyanate transformation assay showed that the thiocyanate formation capacity of the strains after a 12 h incubation ranged from 4.42 to 25.49 mg hydrogen CN equivalent/L. In addition, thiocyanate degradation resulted in the production of ammonia nitrogen and acetic acid in different strains. This study showed that certain strains of enterococci substantially contribute to CN metabolism in ruminants. Our results may serve as a starting point for research aimed at improving ruminant production systems in relation to CN metabolism.

Biomimetic Carbon Sequestration and Cyanate Detoxification Using Heat-Purified Carbonic Anhydrase from Sulfurihydrogenibium yellowstonense

The reaction condition for purifying carbonic anhydrase from Sulfurihydrogenibium yellowstonense (SspCA) by direct heating without prior cell lysis was optimized; heating at 70 °C for 5 min resulted in the highest total activity of 23,460 WAU (Wilbur-Anderson unit) from a 50 mL culture. Heat-purified SspCA was examined for its capability to increase the rate of the mineralization of CO2; compared with an uncatalyzed control, the onset time of CaCO3 formation was shortened by up to 71%. Cyanase can be used to degrade toxic cyanate; however, one of the limitations of this biomimetic process is that the reaction needs HCO3- as a substrate. Heat-purified SspCA was combined with heat-purified cyanase from Thermomyces lanuginosus to alleviate the HCO3- dependence; in industrial wastewater, the HCO3- required was reduced by 50% when 0.75 WAU of SspCA was added. Heat-purified SspCA is stable at 4 °C; 88% of the initial activity was retained for up to five weeks. Partially purified SspCA can be obtained with ease and applied to a variety of applications.

AIE active luminous dye with a triphenylamine attached benzothiazole core as a portable polymer film for sensitively detecting CN- ions in food samples

Aggregation-induced emission (AIE) active 3-(3-(benzo[d]thiazol-2-yl)-2-hydroxyphenyl)-2-(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl)acrylonitrile (BTPA) has been designed and synthesized herein, with the goal of detecting CN^- ions at a low-level in semi-aqueous medium. The deliberate addition of the electron-deficient alkene BTPA increased its sensitivity and selectivity to CN^- ions, with a better detection limit of 6.4 nM, unveiling the next-generation approach to creating sophisticated CN^- ions selective chemosensors. The ESI-MS and NMR spectra analyses provided strong support for the structures of the chemosensors, while the UV-Vis, photoluminescence, and ¹H-NMR titration experiments provided support for the sensing efficiencies. Subsequently, PVDF/BTPA electrospun nanofibers have been effectively produced as functional films. These nanofiber films exhibit outstanding mechanical strength, photo/thermal stability, and optical responsiveness to CN^- ions, making them a potential choice for on-field emerging contaminant detection.

Development of immobilized novel fungal consortium for the efficient remediation of cyanide-contaminated wastewaters

Free cyanide is a hazardous pollutant released from steel industries. Environmentally-safe remediation of cyanide-contaminated wastewater is required. In this work, Pseudomonas stutzeri (ASNBRI_B12), Trichoderma longibrachiatum (ASNBRI_F9), Trichoderma saturnisporum (ASNBRI_F10) and Trichoderma citrinoviride (ASNBRI_F14) were isolated from blast-furnace wastewater and activated-sludge by enrichment culture. Elevated microbial growth, rhodanese activity (82 %) and GSSG (128 %) were observed with 20 mg-CN L^-1. Cyanide degradation > 99 % on 3rd d as evaluated through ion chromatography, followed by first-order kinetics (r² = 0.94-0.99). Cyanide degradation in wastewater (20 mg-CN L^-1, pH 6.5) was studied in ASNBRI_F10 and ASNBRI_F14 which displayed increased biomass to 49.7 % and 21.6 % respectively. Maximum cyanide degradation of 99.9 % in 48 h was shown by an immobilized consortium of ASNBRI_F10 and ASNBRI_F14. FTIR analysis revealed that cyanide treatment alters functional groups on microbial cell walls. The novel consortium of T. saturnisporum-T. citrinoviride in the form of immobilized culture can be employed to treat cyanide-contaminated wastewater.

Recent Progress in the Production of Cyanide-Converting Nitrilases—Comparison with Nitrile-Hydrolyzing Enzymes

Nitrilases have a high potential for application in organic chemistry, environmental technology, and analytics. However, their industrial uses require that they are produced in highly active and robust forms at a reasonable cost. Some organic syntheses catalyzed by nitrilases have already reached a high level of technological readiness. This has been enabled by the large-scale production of recombinant catalysts. Despite some promising small-scale methods being proposed, the production of cyanide-converting nitrilases (cyanide hydratase and cyanide dihydratase) is lagging in this regard. This review focuses on the prospects of cyanide(di)hydratase-based catalysts. The current knowledge of these enzymes is summarized and discussed in terms of the origin and distribution of their sequences, gene expression, structure, assays, purification, immobilization, and uses. Progresses in the production of other nitrilase catalysts are also tackled, as it may inspire the development of the preparation processes of cyanide(di)hydratases.

Ensiling Cyanide Residue and In Vitro Rumen Fermentation of Cassava Root Silage Treated with Cyanide-Utilizing Bacteria and Cellulase

Cyanide is a strong toxin in many tropical forage plants that can negatively affect ruminants. The aim of this study is to determine the cyanide removal efficiency, silage quality, and in vitro rumen fermentation of fresh cassava roots ensiled without an additive (control) and with Acremonium cellulase (AC), two cyanide-utilizing bacterial inoculants (Enterococcus feacium KKU-BF7 (BF7) and E. gallinarum KKU-BC10 (BC10)), and their combinations (BF7 + BC10, AC + BF7, AC + BC10 and AC + BF7 + BC10). A completely randomized design was used with eight treatments × four small-scale silo replicates. Additionally, extra silage samples (seven silos/treatment for individually opening after 0, 1, 3, 5, 7, 15, and 30 days of ensiling) were added to observe the changes in the total cyanide concentration and pH value. The fresh cassava root contained an optimal number of lactic acid bacteria (105 colony forming units/g fresh matter), and the contents of dry matter (DM) and total cyanides were 30.1% and 1304 mg/kg DM, respectively. After 30 days of ensiling, all silages demonstrated a low pH (<3.95; p < 0.01). Cyanide content ranged from 638 to 790 mg/kg DM and was highest in the control (p < 0.01). The addition of BF7 + BC10 increased the crude protein (CP) content (p < 0.01). The addition of AC decreased the fibrous contents (p < 0.01). The control had less acetic acid and propionic acid contents (p < 0.01) and a greater butyric acid content (p < 0.01). However, the degrees of in vitro DM digestibility (IVDMD) and gas production were similar among treatments. Methane production ranged between 29.2 and 33.3 L/kg IVDMD (p < 0.05), which were observed in the AC + BC10 and BF7 + BC10 treatments, respectively. Overall, our results suggested that the cyanide removal efficiency after 30 days of ensiling with good-quality cassava-root silage was approximately 39% of the initial value. The enterococci inoculants and/or AC could improve the ensiling process and cyanide removal efficiency (increasing it to between 47 and 51% of the initial value). The novel enterococci inoculants (BF7 + BC10) were associated with a decreased cyanide content and an increased CP content. They appeared to promote the methanogenesis potential of the cassava root silage. More research is required to validate the use of cyanide-utilizing bacterial inoculants in cyanogenetic plants, bioenergy fermentation, and livestock.

Cyanate Degradation in Different Matrices Using Heat-Purified Enzymes

A green and low-cost removal method for cyanate, a toxic byproduct from the treatment of cyanide, is still needed. Cyanase converts cyanate to CO2 and NH3, but its industrial practicality is limited because the reaction requires HCO3− as a substrate. In this study, we used carbonic anhydrase from Sulfurihydrogenibium azorense (SazCA) to provide HCO3− for cyanase from Thermomyces lanuginosus (TlCyn); both TlCyn and SazCA were purified by one-step heating without prior cell lysis. The heat treatment resulted in higher activities of both enzymes than the conventional two-step process. From a 50 mL-culture, the highest total activity of 147 U and 47,174 WAU was obtained from 5 min of heating at 60 and 80 °C for TlCyn and SazCA, respectively. The coupled enzymatic system was used to degrade cyanate in three different matrices: 50 mM Tris-HCl (pH 8), industrial wastewater, and artificial wastewater. In the industrial wastewater, with the addition of 0.75 WAU (Wilbur-Anderson unit) of SazCA, cyanate degradation using 0.5 mM NaHCO3 was similar to that using 3 mM NaHCO3, indicating an 83% reduction in NaHCO3. We have demonstrated that the dependence on HCO3− of cyanate degradation can be effectively alleviated by using low-cost heat-purified TlCyn and SazCA; the industrial practicality of the coupled enzymatic system is therefore improved.

Treatment of thiocyanate-containing wastewater: a critical review of thiocyanate destruction in industrial effluents

Thiocyanate is a common pollutant in gold mine, textile, printing, dyeing, coking and other industries. Therefore, thiocyanate in industrial wastewater is an urgent problem to be solved. This paper reviews the chemical properties, applications, sources and toxicity of thiocyanate, as well as the various treatment methods for thiocyanate in wastewater and their advantages and disadvantages. It is emphasized that biological systems, ranging from laboratory to full-scale, are able to successfully remove thiocyanate from factories. Thiocyanate-degrading microorganisms degrade thiocyanate in autotrophic manner for energy, while other biodegrading microorganisms use thiocyanate as a carbon or nitrogen source, and the biochemical pathways and enzymes involved in thiocyanate metabolism by different bacteria are discussed in detail. In the future, degradation mechanisms should be investigated at the molecular level, with further research aiming to improve the biochemical understanding of thiocyanate metabolism and scaling up thiocyanate degradation technologies from the laboratory to a full-scale.

Insights into the Metabolomic Capacity of Podaxis and Isolation of Podaxisterols A-D, Ergosterol Derivatives Carrying Nitrosyl Cyanide-Derived Modifications

Cultures of a termite-associated and a free-living member of the fungal genus Podaxis, revived from spores maintained in century-old herbarium collections, were analyzed for their insecticidal and antimicrobial effects. Their secondary metabolomes were explored to uncover possible adaptive mechanisms of termite association, and dereplication of LC-HRMS/MS data sets led to the isolation of podaxisterols A-D (1-4), modified ergosterol derivatives that result from a Diels-Alder reaction with endogenous nitrosyl cyanide. Chemical structures were determined based on HRMS/MS and NMR analyses as well as X-ray crystallography. The putative origin of the endogenous fungal nitrosyl cyanide and ergosterol derivatives is discussed based on results obtained from stable isotope experiments and in silico analysis. Our "omics"-driven analysis of this underexplored yet worldwide distributed fungal genus builds a foundation for studies on a potential metabolic adaptations to diverse lifestyles.

Enhancing Free Cyanide Photocatalytic Oxidation by rGO/TiO2 P25 Composites

Graphene-TiO₂ composites have been investigated in various photocatalytic reactions showing successful synergy compared to pristine TiO₂. In the present work, graphene oxide (GO) was synthesized by the Hummers method and then reduced graphene oxide-TiO₂ composites (rGO/TiO₂) were obtained by an in situ GO photoreduction route. X-ray diffraction, FTIR, Raman, UV–vis DRS, and photoluminescence were the main characterization techniques. The obtained composites containing 1 and 3 wt.% rGO were evaluated in the cyanide (50 mg/L) oxidation and Au-cyanide complex (300 mg/L) degradation under UV-A light. The composites showed higher photocatalytic activity than TiO₂, mainly with the 1% rGO content. Cyanate and gold nanoparticles, deposited on the photocatalyst’s surface, were the main byproducts during the photocatalyst assessment. The improved photocatalytic activity of the composites was attributed to a higher rate of electron transfer and a lower rate of charge recombination due to the chemical interaction of rGO with TiO₂.

Thiosulfate-Cyanide Sulfurtransferase a Mitochondrial Essential Enzyme: From Cell Metabolism to the Biotechnological Applications

Thiosulfate: cyanide sulfurtransferase (TST), also named rhodanese, is an enzyme widely distributed in both prokaryotes and eukaryotes, where it plays a relevant role in mitochondrial function. TST enzyme is involved in several biochemical processes such as: cyanide detoxification, the transport of sulfur and selenium in biologically available forms, the restoration of iron–sulfur clusters, redox system maintenance and the mitochondrial import of 5S rRNA. Recently, the relevance of TST in metabolic diseases, such as diabetes, has been highlighted, opening the way for research on important aspects of sulfur metabolism in diabetes. This review underlines the structural and functional characteristics of TST, describing the physiological role and biomedical and biotechnological applications of this essential enzyme.

Extending the benefits of PGPR to bioremediation of nitrile pollution in crop lands for enhancing crop productivity

Incessant release of nitrile group of compounds such as cyanides into agricultural land through industrial effluents and excessive use of nitrile pesticides has resulted in increased nitrile pollution. Release of nitrile compounds (NCs) as plant root exudates is also contributing to the problem. The released NCs interact with soil elements and persists for a long time. Persistent higher concentration of NCs in soil cause toxicity to beneficial microflora and affect crop productivity. The NCs can cause more problems to human health if they reach groundwater and enter the food chain. Nitrile degradation by soil bacteria can be a solution to the problem if thoroughly exploited. However, the impact of such bacteria in plant and soil environments is still not properly explored. Plant growth-promoting rhizobacteria (PGPR) with nitrilase activity has recently gained attention as potential solution to address the problem. This paper reviews the core issue of nitrile pollution in soil and the prospects of application of nitrile degrading bacteria for soil remediation, soil health improvement and plant growth promotion in nitrile-polluted soils. The possible mechanisms of PGPR that can be exploited to degrade NCs, converting them into plant useful compounds and synthesis of the phytohormone IAA from degraded NCs are also discussed at length.

Diagnosis of lethal cyanide poisoning. Analysis by Anion-Exchange Chromatography with Pulsed Amperometric Detection

Cyanide is a poison widely used in cases of suicide or homicide. Although various methods to identify and quantify this substance are reported in the literature, they are mainly validated on biological fluids (e.g., blood and urine). In the present study, the Anion‐Exchange Liquid Chromatography with Pulsed Amperometric Detection (IC‐PAD) method was validated on blood and, for the first time, on gastric content, and organs (brain, lung, and liver). For each matrix, linearity, accuracy, precision, limit of detection (LOD), lower limit of quantification (LLOQ), matrix interferences, and carryover were assessed. The samples were extracted by steam distillation in acid environment for the following analysis by IC‐PAD. Furthermore, cyanide values found in two real poisoning cases are reported. For each investigated matrix, the analytical method satisfied all acceptance criteria for validation: it showed a good precision and accuracy, selectivity, and sensitivity with no carryover and matrix interference. The extraction by steam distillation in acid environment REDUCED the interference of the matrices and ALLOWED to perform the analysis with good precision and accuracy. In case #1, analysis showed a blood cyanide concentration of 0.99 μg/ml. In case #2, cyanide concentrations were 1.3 μg/g in brain, 0.8 μg/g in lung, 1.6 μg/g in liver, and 1.2 μg/g in gastric content. The cyanide concentrations found in the two reported cases have been suitable to cause death by poisoning.

Plastic Waste Management in India: Challenges, Opportunities, and Roadmap for Circular Economy

Plastic waste (PW) is one of the most rapid-growing waste streams in municipal solid waste all over the world. India has become a global player in the plastic value chain. Despite low consumption, domestic generation and imports create a significant burden on the overall waste management system, which requires in-depth understanding of the scenario and pathways that can mitigate the crisis. Although Indian researchers have widely researched technology-related issues in academic papers, a substantial knowledge gap exists in understanding the problem’s depth and possible solutions. This review article focuses on current plastic production, consumption, and waste generation in India. This review article mainly analyzes data and information regarding Indian PW management and highlights some critical issues such as reverse supply chain, effective PW management, source-specific recovery, and PW rules in India. Comprehensively, this review will help to identify implementable strategies for policymakers and research opportunities for future researchers in holistic PW management and recycling in India, focusing on the circular economy and sustainable development goals.

Isolation of cyanide-degrading bacteria and molecular characterization of its cyanide-degrading nitrilase

Hydrogen cyanide is an industrially important chemical, and its annual production is more than 1.5 million tons. Because of its toxicity, the cyanide-containing effluents from industries have caused many environmental problems. Among various methods to treat the contaminated soils or water, the biological degradation is regarded to be promising. We isolated two cyanide-degrading microorganisms, Pedobacter sp. EBE-1 and Bacillus sp. EBE-2, from soil contaminated with cyanide. Among these bacteria, Bacillus sp. EBE-2 exhibited significantly a high cyanide-degrading ability. Bacillus sp. EBE-2 might be used for the remediation of cyanide contaminated water or soil. A nitrilase gene was cloned from Bacillus sp. EBE-2. Bacillus nitrilase was expressed in Escherichia coli and purified. Bacillus nitrilase exhibited cyanide-degrading activity as a large oligomer. Since formic acid formation from cyanide was observed, Bacillus nitrilase is likely to be a cyanide hydrolase. Although there exist various homologous enzymes annotated as carbon-nitrogen family hydrolases, this is the first report on the cyanide degrading activity. The structure and catalytic site of Bacillus nitrilase were studied by homology modeling and molecular docking simulation.

Computational Design of Nitrile Hydratase from Pseudonocardia thermophila JCM3095 for Improved Thermostability

High thermostability and catalytic activity are key properties for nitrile hydratase (NHase, EC 4.2.1.84) as a well-industrialized catalyst. In this study, rational design was applied to tailor the thermostability of NHase from Pseudonocardia thermophila JCM3095 (PtNHase) by combining FireProt server prediction and molecular dynamics (MD) simulation. Site-directed mutagenesis of non-catalytic residues provided by the rational design was subsequentially performed. The positive multiple-point mutant, namely, M10 (αI5P/αT18Y/αQ31L/αD92H/βA20P/βP38L/βF118W/βS130Y/βC189N/βC218V), was obtained and further analyzed. The Melting temperature (T_m) of the M10 mutant showed an increase by 3.2 °C and a substantial increase in residual activity of the enzyme at elevated temperatures was also observed. Moreover, the M10 mutant also showed a 2.1-fold increase in catalytic activity compared with the wild-type PtNHase. Molecular docking and MD simulations demonstrated better substrate affinity and improved thermostability for the mutant.

Nitrilase: a promising biocatalyst in industrial applications for green chemistry

Nitrilases are widely distributed in nature and are able to hydrolyze nitriles into their corresponding carboxylic acids and ammonia. In industry, nitrilases have been used as green biocatalysts for the production of high value-added products. To date, biocatalysts are considered to be important alternatives to chemical catalysts due to increasing environmental problems and resource scarcity. This review provides an overview of recent advances of nitrilases in aspects of distribution, enzyme screening, molecular structure and catalytic mechanism, protein engineering, and their potential applications in industry.

High Regioselectivity Production of 5-Cyanovaleramide from Adiponitrile by a Novel Nitrile Hydratase Derived from Rhodococcus erythropolis CCM2595

5-Cyanovaleramide (5-CVAM) is an important intermediate of a herbicide and chemical raw material. Herein, we found a novel nitrile hydratase from the strain Rhodococcus erythropolis CCM2595, exhibiting high regioselectivity with higher substrate specificity toward dinitriles than mononitriles. In the past, the strain was shown to degrade only phenol, hydroxybenzoate, p-chlorophenol, aniline, and other aromatic compounds. In our study, 20 mM adiponitrile was completely consumed within 10 min with 95% selectivity to 5-CVAM and 5% selectivity to adipamide. In addition to its high regioselectivity, our recombinant Escherichia coli showed a higher substrate tolerance of up to 200 mM adiponitrile even after 3 h when compared with two reported strains with their cyano-tolerance concentrations of up to 100 mM, which is considered to be the highest cyano-tolerance. Such a robust biocatalyst is a desirable attribute of a biocatalyst intended for use in commercial applications of 5-CVAM.

Molecular mechanisms in phytoremediation of environmental contaminants and prospects of engineered transgenic plants/microbes

Concerns about emerging environmental contaminants have been growing along with industrialization and urbanization around the globe. Among various options for remediating these contaminants, phytotechnology is suggested as a feasible option to maintain the environmental sustainability. The recent advances in phytoremediation, genetic/molecular/omics/metabolic engineering, and nanotechnology are opening new paths for efficient treatment of emerging organic/inorganic contaminants. In this respect, elucidation of molecular mechanisms and genetic engineering of hyperaccumulator plants is expected to enhance remediation of environmental contaminants. This review was organized to offer valuable insights into the molecular mechanisms of phytoremediation and the prospects of transgenic hyperaccumulators with enhanced stress tolerance to diverse contaminants such as heavy metals and metalloids, xenobiotics, explosives, poly aromatic hydrocarbons (PAHs), petroleum hydrocarbons, pesticides, and nanoparticles. The roles of genoremediation and nanoparticles in augmenting the phytoremediation technology are also described in an interrelated framework with biotechnological prospects (e.g., plant molecular nano-farming). Finally, political debate on the preferential use of crops versus non-crop hyperaccumulators in genoremediation, limitations of transgenics in phytotechnologies, and their public acceptance issues are discussed in the policy framework.

Sustainable Approach to Eradicate the Inhibitory Effect of Free-Cyanide on Simultaneous Nitrification and Aerobic Denitrification during Wastewater Treatment

Simultaneous nitrification and aerobic denitrification (SNaD) is a preferred method for single stage total nitrogen (TN) removal, which was recently proposed to improve wastewater treatment plant design. However, SNaD processes are prone to inhibition by toxicant loading with free cyanide (FCN) possessing the highest inhibitory effect on such processes, rendering these processes ineffective. Despite the best efforts of regulators to limit toxicant disposal into municipal wastewater sewage systems (MWSSs), FCN still enters MWSSs through various pathways; hence, it has been suggested that FCN resistant or tolerant microorganisms be utilized for processes such as SNaD. To mitigate toxicant loading, organisms in SNaD have been observed to adopt a diauxic growth strategy to sequentially degrade FCN during primary growth and subsequently degrade TN during the secondary growth phase. However, FCN degrading microorganisms are not widely used for SNaD in MWSSs due to inadequate application of suitable microorganisms (Chromobacterium violaceum, Pseudomonas aeruginosa, Thiobacillus denitrificans, Rhodospirillum palustris, Klebsiella pneumoniae, and Alcaligenes faecalis) commonly used in single-stage SNaD. This review expatiates the biological remedial strategy to limit the inhibition of SNaD by FCN through the use of FCN degrading or resistant microorganisms. The use of FCN degrading or resistant microorganisms for SNaD is a cost-effective method compared to the use of other methods of FCN removal prior to TN removal, as they involve multi-stage systems (as currently observed in MWSSs). The use of FCN degrading microorganisms, particularly when used as a consortium, presents a promising and sustainable resolution to mitigate inhibitory effects of FCN in SNaD.