Exploring anaerobic environments for cyanide and cyano-derivatives microbial degradation

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.

A Reversible Fluorescent Chemosensor for the Selective Detection of Cu2+ and CN- ions by Displacement Approach

A novel fluorescence chemosensor BDP (2-(1-(benzothiazol-2-yl)-5-(4-(diphenylamino)phenyl)-4,5-dihydro-1H-pyrazol-3-yl)phenol) has been synthesized and its sensing behavior has been screened towards various cations by absorption, emission and mass spectroscopic techniques. The probe BDP detects Cu2+ ions preferentially over other metal ions, and the resulting BDP-Cu2+ ensemble acts as a secondary sensor for cyanide anion detection over other anions. The fluorescence intensity of the probe BDP is quenched when it comes into contact with Cu2+ ions, but it is increased reversibly when it comes into contact with cyanide anion, according to spectroscopic measurements. Along with this, optical studies indicate that the sensor BDP has capability to sense Cu2+ and CN- ions selectively over other examined competitive ions with the LOD of 2.57×10-8 M and 2.98×10-8 M respectively. The detection limit of Cu2+ ions is lower than the WHO recommended Cu2+ ions concentration (31.5 µM) in drinking water. On the basis of "on-off-on" fluorescence change of the probe BDP upon interaction with Cu2+ and CN- ions, a possible mechanism for this selective sensing behavior was presented and IMPLICATION logic gate was successfully designed. Furthermore, cell imaging investigations were used to investigate the probe BDP's biological applicability.

Batch and semi-continuous treatment of cassava wastewater using microbial fuel cells and metataxonomic analysis

The treatment of agroindustrial wastewater using microbial fuel cells (MFCs) is a technological strategy to harness its chemical energy while simultaneously purifying the water. This manuscript investigates the organic load effect as chemical oxygen demand (COD) on the production of electricity during the treatment of cassava wastewater by means of a dual-chamber microbial fuel cell in batch mode. Additionally, specific conditions were selected to evaluate the semi-continuous operational mode. The dynamics of microbial communities on the graphite anode were also investigated. The maximum power density delivered by the batch MFC (656.4 μW m- 2 ) was achieved at the highest evaluated organic load (6.8 g COD L- 1 ). Similarly, the largest COD removal efficiency (61.9%) was reached at the lowest organic load (1.17 g COD L- 1 ). Cyanide degradation percentages (50-70%) were achieved across treatments. The semi-continuous operation of the MFC for 2 months revealed that the voltage across the cell is dependent on the supply or suspension of the organic load feed. The electrode polarization resistance was observed to decreases over time, possibly due to the enrichment of the anode with electrogenic microbial communities. A metataxonomic analysis revealed a significant increase in bacteria from the phylum Firmicutes, primarily of the genus Enterococcus.

A prebiotic Krebs cycle analog generates amino acids with H2 and NH3 over nickel

Hydrogen (H2) has powered microbial metabolism for roughly 4 billion years. The recent discovery that it also fuels geochemical analogs of the most ancient biological carbon fixation pathway sheds light on the origin of metabolism. However, it remains unclear whether H2 can sustain more complex nonenzymatic reaction networks. Here, we show that H2 drives the nonenzymatic reductive amination of six biological ketoacids and glyoxylate to give the corresponding amino acids in good yields using ammonium concentrations ranging from 6 to 150 mM. Catalytic amounts of nickel or ground meteorites enable these reactions at 22°C and pH 8. The same conditions promote an H2-dependent ketoacid-forming reductive aldol chemistry that co-occurs with reductive amination, producing a continuous reaction network resembling amino acid synthesis in the metabolic core of ancient microbes. The results support the hypothesis that the earliest biochemical networks could have emerged without enzymes or RNA.

Organic Input to Titan's Subsurface Ocean Through Impact Cratering

Titan has an organic-rich atmosphere and surface with a subsurface liquid water ocean that may represent a habitable environment. In this work, we determined the amount of organic material that can be delivered from Titan's surface to its ocean through impact cratering. We assumed that Titan's craters produce impact melt deposits composed of liquid water that can founder in its lower-density ice crust and estimated the amount of organic molecules that could be incorporated into these melt lenses. We used known yields for HCN and Titan haze hydrolysis to determine the amount of glycine produced in the melt lenses and found a range of possible flux rates of glycine from the surface to the subsurface ocean. These ranged from 0 to 1011 mol/Gyr for HCN hydrolysis and from 0 to 1014 mol/Gyr for haze hydrolysis. These fluxes suggest an upper limit for biomass productivity of ∼103 kgC/year from a glycine fermentation metabolism. This upper limit is significantly less than recent estimates of the hypothetical biomass production supported by Enceladus's subsurface ocean. Unless biologically available compounds can be sourced from Titan's interior, or be delivered from the surface by other mechanisms, our calculations suggest that even the most organic-rich ocean world in the Solar System may not be able to support a large biosphere.

First insight into the natural biodegradation of cyanide in a gold tailings environment enriched in cyanide compounds

The disposal of mining wastes that contain cyanide are dumped in tailings from gold extraction is a public concern in mining countries such as South Africa. Many studies have shown the potential of microorganisms to degrade cyanide. However, no in-situ exploration, in tailings contaminated with cyanide, of the capability of indigenous microorganisms to act as a natural barrier for cyanide attenuation has been performed. Here we aim to combine geochemical and metagenomics techniques to reveal the genomic machinery of indigenous bacteria to degrade cyanide in gold tailings. Indigenous bacteria (i.e., Alicyclobacillus, Sulfobacillus, Acinetobacter, Achromobacter, and among others) pose the genomic machinery to trigger hydrolytic cyanide degradation using enzymes such as nitrilase, nitrile hydratase (Nhase) and thiocyanate. It seems that the lack of nitrogen sources induces the use of cyanide, which would contribute to its natural attenuation in the gold tailings. Therefore, the bacteria identified could represent the first barrier for the detoxification and degradation of cyanide in the outermost layer of the tailings.

Quantifying the energy-material-pollution nexus in a typical fine chemical industry: A sustainable development-oriented support for collaborative emission reduction

The fine chemical industry is currently facing challenges in energy saving, material conservation, and pollution reduction due to the dual policy pressure of precise system management and collaborative pollution and carbon reduction. However, the interweaving of materials and energy input-output was not well understood due to the incomplete coverage and the lack of a generic framework. Therefore, a methodology based on the energy-material-pollution (E-M-P) coupling nexus was proposed to quantitatively assess multi-level coupling. According to the selected generic 32 coupling units, two representative glyphosate (PMG) production processes were taken as case studies. Quantification results showed that the solvent element and the material system had a higher priority. Moreover, Process 2 owned a greater optimization potential as the coupling relationship pairs were 2.55 compared to 2.32 for Process 1, and the correlation proportions of material systems reached 69.26 % and 56.92 %, respectively. In addition, assessment results indicated that Process 2 was more environmentally friendly because of the lower ecological indexes (9.7 GPt vs. 15.8 GPt) and weaker carbon footprint (CF) (1.16E+08 vs. 2.32E+08). Combined coupling nexus and environmental assessment organically, methanol had the most optimization potential and was beneficial for the measures such as solvent substitution. This work offered theory and practice guidance with demonstrative value to support the sustainable development of precise system management.

Emerging contaminants bioremediation by enzyme and nanozyme-based processes - A review

Due to their widespread occurrence and the inadequate removal efficiencies by conventional wastewater treatment plants, emerging contaminants (ECs) have recently become an issue of great concern. Current ongoing studies have focused on different physical, chemical, and biological methods as strategies to avoid exposing ecosystems to significant long-term risks. Among the different proposed technologies, the enzyme-based processes rise as green biocatalysts with higher efficiency yields and lower generation of toxic by-products. Oxidoreductases and hydrolases are among the most prominent enzymes applied for bioremediation processes. The present work overviews the state of the art of recent advances in enzymatic processes during wastewater treatment of EC, focusing on recent innovations in terms of applied immobilization techniques, genetic engineering tools, and the advent of nanozymes. Future trends in the enzymes immobilization techniques for EC removal were highlighted. Research gaps and recommendations on methods and utility of enzymatic treatment incorporation in conventional wastewater treatment plants were also discussed.

Faujasite-Type Zeolite Obtained from Ecuadorian Clay as a Support of ZnTiO3/TiO2 NPs for Cyanide Removal in Aqueous Solutions

In this study, zeolites prepared by the hydrothermal method from Ecuadorian clay were combined with the precursor clay and with the semiconductor ZnTiO₃/TiO₂ prepared by the sol-gel method to adsorb and photodegrade cyanide species from aqueous solutions. These compounds were characterized by X-ray powder diffraction, X-ray fluorescence, scanning electron microscopy, energy-dispersive X-rays, point of zero charge, and specific surface area. The adsorption characteristics of the compounds were measured using batch adsorption experiments as a function of pH, initial concentration, temperature, and contact time. The Langmuir isotherm model and the pseudo-second-order model fit the adsorption process better. The equilibrium state in the reaction systems at pH = 7 was reached around 130 and 60 min in the adsorption and photodegradation experiments, respectively. The maximum cyanide adsorption value (73.37 mg g^-1) was obtained with the ZC compound (zeolite + clay), and the maximum cyanide photodegradation capacity (90.7%) under UV light was obtained with the TC compound (ZnTiO₃/TiO₂ + clay). Finally, the reuse of the compounds in five consecutive treatment cycles was determined. The results reflect that the compounds synthesized and adapted to the extruded form could potentially be used for the removal of cyanide from wastewater.

Molecular level insight of thiocyanate degradation by Pseudomonas putida TDB-1 under a high arsenic and alkaline condition

It is a big challenge to bioremediate thiocyanate pollution in the gold extraction heap leaching tailings and surrounding soils with high contents of arsenic and alkali. Here, a novel thiocyanate-degrading bacterium Pseudomonas putida TDB-1 was successfully applied to completely degrade 1000 mg/L thiocyanate under a high arsenic (400 mg/L) and alkaline condition (pH = 10). It also leached the contents of thiocyanate from 1302.16 to 269.72 mg/kg in the gold extraction heap leaching tailings after 50 h. The maximum transformation rates of S and N in thiocyanate to the two finial products of SO₄^2- and NO₃^- were 88.98 % and 92.71 %, respectively. Moreover, the genome sequencing confirmed that the biomarker gene of thiocyanate-degrading bacterium, CynS was identified in the strain TDB-1. The bacterial transcriptome revealed that critical genes, such as CynS, CcoNOQP, SoxY, tst, gltBD, arsRBCH and NhaC, etc. in the thiocyanate degradation, S and N metabolisms, and As and alkali resistance were significantly up-regulated in the groups with 300 mg/L SCN^- (T300) and with 300 mg/L SCN^- and 200 mg/L As (TA300). In addition, the protein-protein interaction network showed that the glutamate synthase encoding by gltB and gltD served as central node to integrate the S and N metabolism pathways with thiocyanate as substrate. The results of our study provide a novel molecular level insight for the dynamic gene expression regulation of thiocyanate degradation by the strain TDB-1 with a severe arsenic and alkaline stress.

Biodegradation of insensitive munition (IM) formulations: IMX-101 and IMX-104 using aerobic granule technology

A laboratory-scale aerobic granular sludge (AGS) sequencing batch bioreactor (SBR) was initiated in this study for the biodegradation of hazardous insensitive munition (IM) formulation constituents; 2,4-dinitroanisole (DNAN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1-nitroguanidine (NQ), and 3-nitro-1,2,4-triazol-5-one (NTO). Efficient (bio)transformation of the influent DNAN and NTO was achieved throughout reactor operation with removal efficiencies greater than 95%. An average removal efficiency of 38.4 ± 17.5% was recorded for RDX. NQ was only slightly removed (3.96 ± 4.15%) until alkalinity was provided in the influent media, which subsequently increased the NQ removal efficiency up to an average of 65.8 ± 24.4%. Batch experiments demonstrated a competitive advantage for aerobic granular biofilms over flocculated biomass for the (bio)transformation DNAN, RDX, NTO, and NQ, as aerobic granules were capable of reductively (bio)transforming each IM compound under bulk aerobic conditions while flocculated biomass could not, thus demonstrating the contribution of inner oxygen-free zones within aerobic granules. A variety of catalytic enzymes were identified in the extracellular polymeric matrix of the AGS biomass. 16 S rDNA amplicon sequencing found Proteobacteria (27.2-81.2%) to be the most abundant phyla, with many genera associated with nutrient removal as well as genera previously described in relation to the biodegradation of explosives or related compounds.

Enhanced removal of metal-cyanide complexes from wastewater by Fe-impregnated biochar: Adsorption performance and removal mechanism

Metal-cyanide complexes are common contaminants in industrial wastewater. Removal of these refractory contaminants is essential before their discharge into the environment. This study investigated a biochar (BC)-based sorbent material that could be applied for the efficient removal of metal-cyanide complexes from wastewater. In consideration of the strong electrostatic repulsion of the pristine BC toward anions, iron-modified BC (Fe-BC) composites were fabricated by a one-step co-pyrolysis of corn straw and FeCl₃ at 600-800 °C. The adsorption performance and corresponding sorption mechanisms of representative metal-cyanide complexes (ferricyanide [Fe(CN)₆]^3- and tetracyanonickelate [Ni(CN)₄]^2-) onto the Fe-BC composites were investigated. The results indicated that the Fe-BC composites had significantly high affinity toward the metal-cyanide complexes, reaching a maximum sorption capacity of 580.96 mg/g for [Fe(CN)₆]^3- and 588.86 mg/g for [Ni (CN)₄]^2-. A mechanistic study revealed that Fe-impregnation during BC fabrication could effectively alter the negatively charged BC surface, forming more functional groups that could interact with the metal-cyanide complexes. Moreover, the transformation of carbon structure promoted the carbothermal reduction process, leading to the formation of various reductive-Fe minerals in the resulting Fe-BC composites. These modification-induced alterations to the surface and structural characteristics of BC were expected to facilitate the adsorption/precipitation of target contaminants. Different sorption mechanisms were proposed for the two metal-cyanide complexes that were the focus of this study. For [Fe(CN)₆]^3-, precipitation by Fe-bearing species in the Fe-BC composites was the major factor controlling [Fe(CN)₆]^3- removal, while for [Ni(CN)₄]^2- hydrogen bonding interactions between surface functional groups (especially hydroxyl (-OH) and carboxyl (-COOH)) and [Ni(CN)₄]^2- were the main factors controlling removal.

Effect of Doping TiO2 NPs with Lanthanides (La, Ce and Eu) on the Adsorption and Photodegradation of Cyanide-A Comparative Study

Free cyanide is a highly dangerous compound for health and the environment, so treatment of cyanide-contaminated water is extremely important. In the present study, TiO₂, La/TiO₂, Ce/TiO₂, and Eu/TiO₂ nanoparticles were synthesized to assess their ability to remove free cyanide from aqueous solutions. Nanoparticles synthesized through the sol-gel method were characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transformed infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and specific surface area (SSA). Langmuir and Freundlich isotherm models were utilized to fit the adsorption equilibrium experimental data, and pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to fit the adsorption kinetics experimental data. Cyanide photodegradation and the effect of reactive oxygen species (ROS) on the photocatalytic process were investigated under simulated solar light. Finally, reuse of the nanoparticles in five consecutive treatment cycles was determined. The results showed that La/TiO₂ has the highest percentage of cyanide removal (98%), followed by Ce/TiO₂ (92%), Eu/TiO₂ (90%), and TiO₂ (88%). From these results, it is suggested that La, Ce, and Eu dopants can improve the properties of TiO₂ as well as its ability to remove cyanide species from aqueous solutions.

Simultaneous determination of volatile phenol, cyanide, anionic surfactant, and ammonia nitrogen in drinking water by a continuous flow analyzer

This study developed a method for the simultaneous determination of volatile phenol, cyanide, anionic surfactant, and ammonia nitrogen in drinking water, using a continuous flow analyzer. The samples were first distilled at 145 °C. The phenol in the distillate then subsequently reacted with alkaline ferricyanide and 4-aminoantipyrine to form a red complex that was measured colorimetrically at 505 nm. Cyanide in the distillate subsequently reacted with chloramine T to form cyanogen chloride, which then formed a blue complex with pyridinecarboxylic acid that was measured colorimetrically at 630 nm. The anionic surfactant reacted with basic methylene blue to form a compound that was extracted into chloroform and washed with acidic methylene blue to remove interfering substances. The blue compound in chloroform was determined colorimetrically at 660 nm. Ammonia reacted with salicylate and chlorine from dichloroisocyanuric acid to produce indophenol blue at 37 °C in an alkaline environment that was measured at 660 nm. The relative standard deviations were 0.75-6.10% and 0.36-5.41%, respectively, and the recoveries were 96.2-103.6% and 96.0-102.4% when the mass concentration of volatile phenol and cyanide was in the range of 2-100 μg/L. The linear correlation coefficients were ≥ 0.9999, and the detection limits were1.2 μg/L and 0.9 μg/L, respectively. The relative standard deviations were 0.27-4.86% and 0.33-5.39%, and the recoveries were 93.7-107.0% and 94.4-101.7%. When the mass concentration of anionic surfactant and ammonia nitrogen was 10-1000 μg/L. The linear correlation coefficients were 0.9995 and 0.9999, and the detection limits were 10.7 μg/L and 7.3 μg/L, respectively. When compared to the national standard method, no statistically significant difference was found. This approach saves time and labor, has a lower detection limit, higher precision and accuracy, less contamination, and is more appropriate for the analysis and determination of large-volume samples.

Effect of Heat Processing of Rubber Seed Kernel on In Vitro Rumen Biohydrogenation of Fatty Acids and Fermentation

The aim of this study was to assess the effect of rubber seed kernel heat processing on in vitro rumen biohydrogenation of fatty acids and fermentation. The experiment was conducted with a completely randomized design (CRD). The inclusion of RSK at 0% (CON) and 20% with different processing methods as follows: Raw rubber seed kernel (RAWR), roasted rubber seed kernel (ROR), microwave irradiated rubber seed kernel (MIR), and rubber seed kernel were heated in a hot air oven (RHO) in total mixed ration (TMR) diets. The hydrogen cyanide (HCN) was reduced using RSK heat methods. The heat processing of RSK had no effect on cumulative gas production at 96 h, the gas production from the insoluble fraction (b), or degradability (p > 0.05), whereas it reduced the gas production from the immediately soluble fraction (a) and constant rate of gas production for the insoluble fraction (c) (p < 0.01). The RSK processing methods did not influence ruminal pH, total volatile fatty acid (VFA), or VFA proportions (p > 0.05). RSK heat processing reduced ammonia-nitrogen (NH3-N) (p < 0.04) while increasing the bacterial population (p < 0.02). Heat treatment had no effect on linoleic acid (C18:2 cis-9,12 + tran-9,12) (p > 0.05). The RHO increases oleic acid (C18:1 cis-9 + tran-9) and linolenic acid (C18:3 cis-9,12,15) concentrations (p < 0.01). In conclusion, RHO reduced rumen biohydrogenation of unsaturated fatty acids (UFA), especially C18:3 and C18:1.

Sustainable bioremediation approach to treat the sago industry effluents and evaluate the possibility of yielded biomass as a single cell protein (SCP) using cyanide tolerant Streptomyces tritici D5

This sustainable approach was performed to evaluate the bioremediation potential of cyanide resistant bacterial species on sago industry effluents and assess the possibility of using the yielded biomass as single cell protein (SCP). The predominant cyanide tolerant bacterium enumerated from muddy soil was identified as Streptomyces tritici D5 through 16S rRNA sequencing. The identified S. tritici D5 strains showed excellent resistant and degradation potential at 100 mM concentration of potassium cyanide. Furthermore, the physicochemical properties analysis of sago industry effluents results revealed that the most of the parameters were crossing the permissible limits of Pollution control board of India. The bioremediation process was performed at various temperatures at 25 °C, 35 °C, and 45 °C for a period of 30 days of continuous bioremediation process with the aid of an aerator. Surprisingly, the best organic pollutant reduction was found at 35 °C and 45 °C, with 25 °C following close behind. Remarkably, the dissolved oxygen (DO) level was gradually increased from 2.24 to 12.04 mg L^-1 at 35 °C in 30 days of the remediation process. The pH and ammonia were also significantly increased during the bioremediation process in 30 days of treatment. Similarly, at 35 °C of bioremediation process the S. tritici D5 yielded maximum dried biomass (6.9 g L^-1) with the total crude protein (SCP) as 4.8 g L^-1 (69.56%) in 30 days of growth. These findings stated that S. tritici D5 can treat sago industry effluents and that the biomass produced may be considered SCP after some in-vitro and in-vivo analyses.

Effect of Cyanide-Utilizing Bacteria and Sulfur Supplementation on Reducing Cyanide Concentration and In Vitro Degradability Using In Vitro Gas Production Technique

The objective of this research was to supplement the cyanide-utilizing bacteria and sulfur in the HCN-rich diet, affecting the gas production and fermentation of rumen in vitro, and lowering the HCN content and the digestion of nutrients. A 2 × 2 × 3 factorial experiment in a completely randomized design was applied during the test. In the experiments, three factors were used. Factor A was the level of CUB at 0 and 108 CFU/mL. Factor B was the level of sulfur in the diet at 0% and 3% of dry matter (DM). Factor C was the three levels of potassium cyanide (KCN) at 0, 300, and 600 ppm. The interaction of CUB × sulfur × KCN affected gas production from the immediately soluble fraction (a) (p < 0.05). However, the greatest ruminal cyanide concentration was found when CUB (with and without), sulfur (3%), and KCN (600 ppm) were introduced at 0 h (p < 0.05). It revealed that the addition of CUB and sulfur had a significant impact on gas accumulation at 96 h (p < 0.05). The addition of CUB with sulfur had an effect on pH at 2 h and ruminal cyanide levels at 6 h (p < 0.05). At 2 h, sulfur supplementation with KCN had an effect on NH3-N (p < 0.01). The addition of sulfur (3%) and KCN (300 ppm) produced the highest ammonia nitrogen. However, the combination of sulfur (3%) and KCN (600 ppm) produced the lowest level of ammonia nitrogen (p < 0.01). CUB supplementation increased the in vitro dry matter digestibility (IVDMD) by 11.16% compared to the without-CUB supplemented group (p < 0.05). Supplementation with 3% sulfur increased the in vitro neutral detergent fiber (IVNDFD) by 16.87% but had no effect on IVDMD or in vitro acid detergent fiber (IVADFD) (p < 0.05). The volatile fatty acid (VFA) such as acetate, propionate, and butyrate were not different when CUB, sulfur, and KCN were added. Doses above 600 ppm had the lowest concentrations of TVFA and propionate (p < 0.01). Based on the results of this investigation, supplementing with CUB and sulfur (3%) may improve cumulative gas, digestibility, and TVAF. Supplementing with CUB, on the other hand, reduced HCN the most, by 54.6%.

An Overview of Emerging Cyanide Bioremediation Methods

Cyanide compounds are hazardous compounds which are extremely toxic to living organisms, especially free cyanide in the form of hydrogen cyanide gas (HCN) and cyanide ion (CN−). These cyanide compounds are metabolic inhibitors since they can tightly bind to the metals of metalloenzymes. Anthropogenic sources contribute significantly to CN− contamination in the environment, more specifically to surface and underground waters. The treatment processes, such as chemical and physical treatment processes, have been implemented. However, these processes have drawbacks since they generate additional contaminants which further exacerbates the environmental pollution. The biological treatment techniques are mostly overlooked as an alternative to the conventional physical and chemical methods. However, the recent research has focused substantially on this method, with different reactor configurations that were proposed. However, minimal attention was given to the emerging technologies that sought to accelerate the treatment with a subsequent resource recovery from the process. Hence, this review focuses on the recent emerging tools that can be used to accelerate cyanide biodegradation. These tools include, amongst others, electro-bioremediation, anaerobic biodegradation and the use of microbial fuel cell technology. These processes were demonstrated to have the possibility of producing value-added products, such as biogas, co-factors of neurotransmitters and electricity from the treatment process.

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.

Cyanide Biodegradation by Trichoderma harzianum and Cyanide Hydratase Network Analysis

Cyanide is a poisonous and dangerous chemical that binds to metals in metalloenzymes, especially cytochrome C oxidase and, thus, interferes with their functionalities. Different pathways and enzymes are involved during cyanide biodegradation, and cyanide hydratase is one of the enzymes that is involved in such a process. In this study, cyanide resistance and cyanide degradation were studied using 24 fungal strains in order to find the strain with the best capacity for cyanide bioremediation. To confirm the capacity of the tested strains, cyano-bioremediation and the presence of the gene that is responsible for the cyanide detoxification was assessed. From the tested organisms, Trichoderma harzianum (T. harzianum) had a significant capability to resist and degrade cyanide at a 15 mM concentration, where it achieved an efficiency of 75% in 7 days. The gene network analysis of enzymes that are involved in cyanide degradation revealed the involvement of cyanide hydratase, dipeptidase, carbon–nitrogen hydrolase-like protein, and ATP adenylyltransferase. This study revealed that T. harzianum was more efficient in degrading cyanide than the other tested fungal organisms, and molecular analysis confirmed the experimental observations.

Cyanide treatment of mining tailings using suspended biomass and moving bed biomass reactors

Mexico is the top producer of silver and is on the eighth place from producing gold in the world. For instance, the hydrometallurgical extraction process produces wastewater (mining tailing) characterized by being composed with varying concentrations of cyanide and heavy metals. The purpose of this research was to study the biodegradation of cyanide contained in mining tailings by means of a bacterial consortium isolated from a tailings dam. For this purpose, three types of Eckendfelder reactors were used, one with suspended biomass (BS) and two moving bed biofilter reactors, one with biomass immobilized on Kaldnes (BK) supports, and the other on polyurethane cubes (BCP). Three experimental stages were worked; in each of them, the concentrations of total cyanide were varied. In the first one, it was 26 ± 2 mg·L^-1; in the second one 40 ± 4 mg·L^-1; and the third one 55 ± 4 mg·L^-1. During the whole operation, the pH and temperature were maintained at 9.5 units and 25 °C. After 141 days of operation, biodegradation of the total cyanide contained in the mining tailings was 69% (17 mg·L^-1) in the BS reactor, while in the BK reactor, it was 93% (3.9 mg·L^-1) and in the BCP reactor 95% (2.5 mg·L^-1). The predominant families in each of the reactors, as well as their respective relative abundances, were for the BS and for the BK of Cyclobacteriaceae (20.65% and 24.64%) and Rhizobiaceae (18.48% and 14.01%) and Halomonadaceae (46.97%) and Hyphomonadaceae (24.94%) in the BCP.

Enhanced anaerobic digestion of tar solution from rice husk thermal gasification with hybrid upflow anaerobic sludge-biochar bed reactor

Tar generated as a by-product during biomass gasification contains a high concentration of refractory organic matters. In this study, a hybrid upflow anaerobic sludge-biochar bed reactor was established for tar treatment, and the methane yield was 120-154 NmL-CH₄/g-COD_inf, 20-30% higher than the control reactor. COD removal and methane production significantly decreased in both reactors when the influent tar concentration was doubled from 4954 mg-COD/L to 9964 mg-COD/L. When the influent concentration was reduced, the biochar packed reactor showed a faster recovery. Batch tests confirmed that higher tar concentration inhibited methane production and induced longer lagphase. Biochar addition effectively relieved the inhibition and prolonged the retention of organic matters. SEM observation and 16S rRNA analysis suggested that biochar also acted as the microbe's carrier, and promoted the growth of some microbes. The results of this study provide new ideas for tar treatment.

Evaluation of N doped rGO-ZnO-CoPc(COOH)8 nanocomposite in cyanide degradation and its bactericidal activities

In the present study, an attempt has been made to design a solar light driven N-rGO-ZnO- CoPc(COOH)₈ nanocomposite for the degradation of cyanide. The morphological and structural characterization of the synthesized nanocomposite was performed by XRD, FT-IR, XPS, UV-vis DRS, FESEM, TEM, EDS, PL spectra and BET surface area. The results revealed that almost 91% degradation and 86% toxicity removal occurred at 25 mgL^-1 of initial cyanide concentration by the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite under illumination of solar light within 120 min. Analysis of free radicals reveals that the generation of OH^. radicals was the predominant species in the photocatalytic degradation process. The cyanide degradation follows pseudo-first order kinetics. The estimated apparent rate constant (K_app) of the above nanocomposite was 3 times higher than that of the ZnO photocatalyst alone together with a very good recycle activities. This might be due to the application of metallpthalocyanine photosensitizer CoPc(COOH)₈ which enhances the rate of visible light absorption efficiency and activates the higher band gap ZnO photocatalyst under visible light. In addition, the presence of residual oxygen in N-rGO also promotes nucleation and anchor sites for interfacial contact between ZnO and N-rGO for effective charge transfer. Further, the N-rGO-ZnO-CoPc(COOH)₈ photocatalytic system showed significant antibacterial activities against mixed culture systems. Therefore, the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite may be an alternative solar light driven photocatalyst system for the removal of cyanide from the wastewater along with its strong disinfectant activities.

Alternative Pathway for 3-Cyanoalanine Assimilation in Pseudomonas pseudoalcaligenes CECT5344 under Noncyanotrophic Conditions

3-Cyanoalanine and cyanohydrins are intermediate nitriles produced in cyanide degradation pathways in plants and bacteria. 3-Cyanoalanine is generated from cyanide by the 3-cyanoalanine synthase, an enzyme mainly characterized in cyanogenic plants. NIT4-type nitrilases use 3-cyanoalanine as a substrate, forming ammonium and aspartate. In some organisms, this enzyme also generates asparagine through an additional nitrile hydratase activity. The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 assimilates cyanide through an intermediate cyanohydrin, which is further converted into ammonium by the nitrilase NitC. This bacterium also contains three additional nitrilases, including Nit4. In this work, a proteomic analysis of P. pseudoalcaligenes CECT5344 cells grown with 3-cyanoalanine as the sole nitrogen source has revealed the overproduction of different proteins involved in nitrogen metabolism, including the nitrilase NitC. In contrast, the nitrilase Nit4 was not induced by 3-cyanoalanine, and it was only overproduced in cells grown with a cyanide-containing jewelry-manufacturing residue. Phenotypes of single and double mutant strains defective in nit4 or/and nitC revealed the implication of the nitrilase NitC in the assimilation of 3-cyanoalanine and suggest that the 3-cyanoalanine assimilation pathway in P. pseudoalcaligenes CECT5344 depends on the presence or absence of cyanide. When cyanide is present, 3-cyanoalanine is assimilated via Nit4, but in the absence of cyanide, a novel pathway for 3-cyanoalanine assimilation, in which the nitrilase NitC uses the nitrile generated after deamination of the α-amino group from 3-cyanoalanine, is proposed. IMPORTANCE Nitriles are organic cyanides with important industrial applications, but they are also found in nature. 3-Cyanoalanine is synthesized by plants and some bacteria to detoxify cyanide from endogenous or exogenous sources, but this nitrile may be also involved in other processes such as stress tolerance, nitrogen and sulfur metabolism, and signaling. The cyanide-degrading bacterium Pseudomonas pseudoalcaligenes CECT5344 grows with 3-cyanoalanine as the sole nitrogen source, but it does not use this nitrile as an intermediate in the cyanide assimilation pathway. In this work, a quantitative proteomic analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to study, for the first time, the response to 3-cyanoalanine at the proteomic level. Proteomic data, together with phenotypes of different nitrilase-defective mutants of P. pseudoalcaligenes CECT5344, provide evidence that in the absence of cyanide, the nitrilase Nit4 is not involved in 3-cyanoalanine assimilation, and instead, the nitrilase NitC participates in a novel alternative 3-cyanoalanine assimilation pathway.

Treatment of neutral gold mine drainage by sequential in situ hydrotalcite precipitation, and microbial sulfate and cyanide removal

This study proposed and validated a method integrating in situ hydrotalcite precipitation (Virtual Curtain™ (VC) technology) with bioprocess for treating a cyanide (CN)-augmented (ca. 5 mg-CN L^-1) sulfate-laden neutral mine drainage, from a waste rock dump (WD2) of an Australian gold mine. Efficacies of various carbon (C) sources (ethanol, lactate, and two natural substrates; Eucalyptus wood sawdust (EW) and Typha biomass (TB)) for promoting microbial reduction in both: CN-augmented WD2 water and VC-treated CN-augmented WD2 water were assessed in a 60-days microcosms study at 30 °C. The microcosms were monitored over time for pH, redox potential, dissolved hydrogen sulfide, chloride, nitrite, nitrate, sulfate, phosphate, biogas production, dissolved organic carbon, total dissolved nitrogen, and dissolved CN. The VC treatment removed a range of metals (Mg, Ni and Zn) and metalloid Se from the CN-augmented WD2 water to below detection. Other elements substantially reduced in concentration included Ba, F, Si and U. However, the VC treatment did not remove substantial nitrate, sulfate or CN. Microcosm trials revealed that the indigenous microbial community in WD2 could effectively denitrify and reduce sulfate, with TB was the most efficient C source for promoting sulfate and CN removal; whereas, EW facilitated only marginally higher sulfate reduction compared with controls. The highest sulfate reduction rate (76 g-SO₄^2- m^-3 d^-1) was achieved with VC-treated water amended with TB, indicating that VC pre-treatment was beneficial. Further, all treatments amended with external C, facilitated 100% removal of dissolved CN after 60 days, whereas only partial (65%) CN removal was recorded in the control. Overall, the proposed integrated method appears a viable option for treating neutral gold mine drainage.

Bioremediation of cyanide-containing wastes: The potential of systems and synthetic biology for cleaning up the toxic leftovers from mining

Synthetic biology could harness the ability of microorganisms to use highly toxic cyanide compounds for growth applied to bioremediation of cyanide-contaminated mining wastes and areas.

Photocatalytic degradation of cyanide using polyurethane foam immobilized Fe-TCPP-S-TiO2-rGO nano-composite

An attempt has been made for the treatment of cyanide contaminated wastewater using a S-TiO₂@rGO heterogeneous photocatalyst system immobilized on polyurethane foam (PUF) supporting materials. Further, to make the photocatalytic system more efficient and active under visible light, a highly efficient iron porphyrin derivative sensitizer viz. Fe-TCPP was synthesized and employed for cyanide degradation. To investigate the synthesized heterogeneous nano-composite S-TiO₂@rGO-FeTCPP photocatalytic system, advanced techniques such as XRD, XPS, FT-IR, PL spectra, UV-vis DRS, FESEM, and EDS were utilized. The photocatalytic performance of the nanocomposite was evaluated in a suspended system and results revealed that about 75% of cyanide degradation was obtained at 100 mg/L of initial cyanide within 2 h. Whereas, at the same condition, more than 91% of cyanide degradation as well as 88% toxicity removal occurred by the PUF immobilized S-TiO2@rGO-FeTCPP solid-state photocatalytic system. First-order kinetics was applied to investigate the degradation of cyanide by the photocatalytic nanocomposite. From the kinetic study, the estimated first-order rate constant (K_f) in a solid-state photocatalytic system of the nanocomposite was 1.7 times superior to that of the suspended system. Further, the rate of photocatalytic activity was nearly 10.8 times greater than that of pure TiO₂. This study demonstrated that the immobilized S-TiO2@rGO-FeTCPP photocatalytic system could be an efficient technique for degrading cyanide from industrial effluent.

Magnetic mesoporous nanomaterials with AIE properties for selective detection and removal of CN- from water under magnetic conditions

We have prepared a type of magnetic mesoporous nanomaterial with aggregation-induced emission properties (Fe₃O₄@mSiO₂@TPA@BA, hence abbr. FSTB) to detect and remove cyanide ions (CN^-) under magnetic conditions. FSTB has a large specific surface area and improved fluorescence performance to identify CN^-, and its superparamagnetic behavior plays an important role in removing CN^-. The magnetic sensor FSTB shows excellent selectivity and anti-interference for the detection of CN^- in aqueous solutions. It is obvious from the equation LOD = 3δ/S that the limit of detection (LOD) of FSTB for CN^- is significantly lower than the permissible level of CN^- in drinkable water recommended by the World Health Organization. Therefore, the magnetic sensor FSTB has a wide range of applications for detecting and removing harmful CN^-.

High-Throughput Volatilome Fingerprint Using PTR-ToF-MS Shows Species-Specific Patterns in Mortierella and Closely Related Genera

In ecology, Volatile Organic Compounds (VOCs) have a high bioactive and signaling potential. VOCs are not only metabolic products, but are also relevant in microbial cross talk and plant interaction. Here, we report the first large-scale VOC study of 13 different species of Mortierella sensu lato (s. l.) isolated from a range of different alpine environments. Proton Transfer Reaction-Time-of-Flight Mass Spectrometry (PTR-ToF-MS) was applied for a rapid, high-throughput and non-invasive VOC fingerprinting of 72 Mortierella s. l. isolates growing under standardized conditions. Overall, we detected 139 mass peaks in the headspaces of all 13 Mortierella s. l. species studied here. Thus, Mortierella s. l. species generally produce a high number of different VOCs. Mortierella species could clearly be discriminated based on their volatilomes, even if only high-concentration mass peaks were considered. The volatilomes were partially phylogenetically conserved. There were no VOCs produced by only one species, but the relative concentrations of VOCs differed between species. From a univariate perspective, we detected mass peaks with distinctively high concentrations in single species. Here, we provide initial evidence that VOCs may provide a competitive advantage and modulate Mortierella s. l. species distribution on a global scale.

Effects of physicochemical properties of Au cyanidation tailings on cyanide microbial degradation

The initial cyanide (CN^-) concentration and amount of co-contaminants in GCTs can inhibit bacterial growth and reduce the CN^--degrading ability of bacteria. Several microorganisms can biotransform a wide range of organic and inorganic industrial contaminants into nontoxic compounds. However, active enzymatic CN^- metabolism processes are mostly constrained by the physical and chemical characteristics of GCTs. High concentrations of toxic metal co-contaminants, such as, Pb, and Cr, and factors, such as pH, temperature, and oxygen concentration create oxidative stress and limit the CN^--degrading potential of cyanotrophic strains. The effects of such external and internal factors on the CN^--degrading ability of bacteria hinder the selection of suitable microorganisms for CN^- biodegradation. Therefore, understanding the effects of the physicochemical properties of GCTs on cyanobacteria strains can help identify suitable microbes and favorable environmental conditions to promote microbial growth and can also help design efficient CN^- biodegradation processes. In this review, we present a detailed analysis of the physicochemical properties of GCTs and their effects on microbial CN^- degradation.

Soehngenia longivitae sp. nov., a Fermenting Bacterium Isolated from a Petroleum Reservoir in Azerbaijan, and Emended Description of the Genus Soehngenia

A methanogenic enrichment growing on a medium with methanol was obtained from a petroleum reservoir (Republic of Azerbaijan) and stored for 33 years without transfers to fresh medium. High-throughput sequencing of the V4 region of the 16S rRNA gene revealed members of the genera Desulfovibrio, Soehngenia, Thermovirga, Petrimonas, Methanosarcina, and Methanomethylovorans. A novel gram-positive, rod-shaped, anaerobic fermentative bacterium, strain 1933PT, was isolated from this enrichment and characterized. The strain grew at 13-55 °C (optimum 35 °C), with 0-3.0% (w/v) NaCl (optimum 0-2.0%) and in the pH range of 6.7-8.0 (optimum pH 7.0). The 16S rRNA gene sequence similarity, the average nucleotide identity (ANI) and in silico DNA-DNA hybridization (dDDH) values between strain 1933PT and the type strain of the most closely related species Soehngenia saccharolytica DSM 12858T were 98.5%, 70.5%, and 22.6%, respectively, and were below the threshold accepted for species demarcation. Genome-based phylogenomic analysis and physiological and biochemical characterization of the strain 1933PT (VKM B-3382T = KCTC 15984T) confirmed its affiliation to a novel species of the genus Soehngenia, for which the name Soehngenia longivitae sp. nov. is proposed. Genome analysis suggests that the new strain has potential in the degradation of proteinaceous components.

Diversity and functional prediction of microbial communities involved in the first aerobic bioreactor of coking wastewater treatment system

The pre-aerobic process of coking wastewater treatment has strong capacity of decarbonization and detoxification, which contribute to the subsequent dinitrogen of non-carbon source/heterotrophic denitrification. The COD removal rate can reach > 90% in the first aerobic bioreactor of the novel O/H/O coking wastewater treatment system during long-term operation. The physico-chemical characteristics of influent and effluent coking wastewater in the first aerobic bioreactor were analyzed to examine how they correlated with bacterial communities. The diversity of the activated sludge microbial community was investigated using a culture-independent molecular approach. The microbial community functional profiling and detailed pathways were predicted from the 16S rRNA gene-sequencing data by the PICRUSt software and the KEGG database. High-throughput MiSeq sequencing results revealed a distinct microbial composition in the activated sludge of the first aerobic bioreactor of the O/H/O system. Proteobacteria, Bacteroidetes, and Chlorobi were the decarbonization and detoxification dominant phyla with the relative abundance of 84.07 ± 5.45, 10.89 ± 6.31, and 2.96 ± 1.12%, respectively. Thiobacillus, Rhodoplanes, Lysobacter, and Leucobacter were the potential major genera involved in the crucial functional pathways related to the degradation of phenols, cyanide, benzoate, and naphthalene. These results indicated that the comprehensive understanding of the structure and function diversity of the microbial community in the bioreactor will be conducive to the optimal coking wastewater treatment.

Role of the Dihydrodipicolinate Synthase DapA1 on Iron Homeostasis During Cyanide Assimilation by the Alkaliphilic Bacterium Pseudomonas pseudoalcaligenes CECT5344

Cyanide is a toxic compound widely used in mining and jewelry industries, as well as in the synthesis of many different chemicals. Cyanide toxicity derives from its high affinity for metals, which causes inhibition of relevant metalloenzymes. However, some cyanide-degrading microorganisms like the alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 may detoxify hazardous industrial wastewaters that contain elevated cyanide and metal concentrations. Considering that iron availability is strongly reduced in the presence of cyanide, mechanisms for iron homeostasis should be required for cyanide biodegradation. Previous omic studies revealed that in the presence of a cyanide-containing jewelry residue the strain CECT5344 overproduced the dihydrodipicolinate synthase DapA1, a protein involved in lysine metabolism that also participates in the synthesis of dipicolinates, which are excellent metal chelators. In this work, a dapA1 ^- mutant of P. pseudoalcaligenes CECT5344 has been generated and characterized. This mutant showed reduced growth and cyanide consumption in media with the cyanide-containing wastewater. Intracellular levels of metals like iron, copper and zinc were increased in the dapA1 ^- mutant, especially in cells grown with the jewelry residue. In addition, a differential quantitative proteomic analysis by LC-MS/MS was carried out between the wild-type and the dapA1 ^- mutant strains in media with jewelry residue. The mutation in the dapA1 gene altered the expression of several proteins related to urea cycle and metabolism of arginine and other amino acids. Additionally, the dapA1 ^- mutant showed increased levels of the global nitrogen regulator PII and the glutamine synthetase. This proteomic study has also highlighted that the DapA1 protein is relevant for cyanide resistance, oxidative stress and iron homeostasis response, which is mediated by the ferric uptake regulator Fur. DapA1 is required to produce dipicolinates that could act as iron chelators, conferring protection against oxidative stress and allowing the regeneration of Fe-S centers to reactivate cyanide-damaged metalloproteins.

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.

Structure and function of microbial community involved in a novel full-scale prefix oxic coking wastewater treatment O/H/O system

A novel full-scale prefix oxic coking wastewater (CWW) biological treatment O/H/O system had been operated steadily six years with the effluent quality meeting national discharge standard. Comparing to the traditional CWW biological treatment process, which usually have an anaerobic unit at the start of the process, here the O/H/O system has obvious advantages in COD removal, total nitrogen removal and reduced energy consumption. It is very necessary to illustrate the structure and function of the microbial community involved in different bioreactors of the O/H/O system. High-throughput MiSeq sequencing was used to examine the 16S rRNA genes in this system. Results revealed a contrasting microbial composition among the activated sludge samples of three sequential bioreactors: the β-Proteobacteria related sequences dominated in the O₁ activated sludge with the relative abundance of 56.44% while 7.53% of the sequences were assigned to Thiobacillus; Rhodoplanes related sequences dominated in the bioreactor H and O₂ activated sludge with relative abundance of 8.86% and 8.92%, respectively. The physico-chemical characteristics of CWW were analyzed by standard methods and the operational parameters were routinely monitored to examine their effects on the microbial communities. The bioinformatics software package of phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was used to predict the microbial community functional profiling and found three dominant genera of Rhodoplanes, Lysobacter and Leucobacter enriched the xenobiotics biodegradation and metabolism pathway. The diverse and distinct microbial community involved in biological treatment processes of CWW treatment indicating that water characteristics and operational parameters determined the microbial community composition. These results significantly expanded our knowledge of the biodiversity and population dynamics of microorganisms and discerned the relationships between bacterial communities and environmental variables in the biological treatment processes. Moreover, in this study, we proposed a comprehensive biodegradation model of CWW treatment and defined as O/H/O system.

Cyanate Assimilation by the Alkaliphilic Cyanide-Degrading Bacterium Pseudomonas pseudoalcaligenes CECT5344: Mutational Analysis of the cyn Gene Cluster

The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 can grow with cyanate, cyanide, or cyanide-containing industrial residues as the sole nitrogen source, but the assimilation of cyanide and cyanate takes place through independent pathways. Therefore, cyanide degradation involves a chemical reaction between cyanide and oxaloacetate to form a nitrile that is hydrolyzed to ammonium by the nitrilase NitC, whereas cyanate assimilation requires a cyanase that catalyzes cyanate decomposition to ammonium and carbon dioxide. The P. pseudoalcaligenes CECT5344 cynFABDS gene cluster codes for the putative transcriptional regulator CynF, the ABC-type cyanate transporter CynABD, and the cyanase CynS. In this study, transcriptional analysis revealed that the structural cynABDS genes constitute a single transcriptional unit, which was induced by cyanate and repressed by ammonium. Mutational characterization of the cyn genes indicated that CynF was essential for cynABDS gene expression and that nitrate/nitrite transporters may be involved in cyanate uptake, in addition to the CynABD transport system. Biodegradation of hazardous jewelry wastewater containing high amounts of cyanide and metals was achieved in a batch reactor operating at an alkaline pH after chemical treatment with hydrogen peroxide to oxidize cyanide to cyanate.

Putative small RNAs controlling detoxification of industrial cyanide-containing wastewaters by Pseudomonas pseudoalcaligenes CECT5344

The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 uses free cyanide and several metal−cyanide complexes as the sole nitrogen source and tolerates high concentrations of metals like copper, zinc and iron, which are present in the jewelry wastewaters. To understand deeply the regulatory mechanisms involved in the transcriptional regulation of cyanide-containing wastewaters detoxification by P. pseudoalcaligenes CECT5344, RNA-Seq has been performed from cells cultured with a cyanide-containing jewelry wastewater, sodium cyanide or ammonium chloride as the sole nitrogen source. Small RNAs (sRNAs) that may have potential regulatory functions under cyanotrophic conditions were identified. In total 20 sRNAs were identified to be differentially expressed when compared the jewelry residue versus ammonium as nitrogen source, 16 of which could be amplified successfully by RT-PCR. As predicted targets of these 16 sRNAs were several components of the nit1C gene cluster encoding the nitrilase NitC essential for cyanide assimilation, the cioAB gene cluster that codes for the cyanide-insensitive cytochrome bd-type terminal oxidase, the medium length-polyhydroxyalkanoates (ml-PHAs) gene cluster, and gene clusters related with a global nitrogen limitation response like those coding for glutamine synthase and urease. Other targets were non-clustered genes (or their products) involved in metal resistance and iron acquisition, such as metal extrusion systems and the ferric uptake regulatory (Fur) protein, and a GntR-like regulatory family member probably involved in the regulation of the cyanide assimilation process in the strain CECT5344. Induction of genes targeted by sRNAs in the jewelry residue was demonstrated by qRT-PCR.

Interplay of nucleophilic catalysis with proton transfer in the nitrile reductase QueF from Escherichia coli

Proton relay through an active-site network of hydrogen bonds promotes enzymatic nitrile reduction to amine via a covalent thioimidate enzyme intermediate.