Enzymatic cyanide degradation by cell-free extract of Rhodococcus UKMP-5M

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.

Rhodococcus: A promising genus of actinomycetes for the bioremediation of organic and inorganic contaminants

Rhodococcus is a genus of actinomycetes that has been explored by the scientific community for different purposes, especially for bioremediation uses. However, the mechanisms governing Rhodococcus-mediated bioremediation processes are far from being fully elucidated. In this sense, this work aimed to compile the recent advances in the use of Rhodococcus for the bioremediation of organic and inorganic contaminants present in different environmental compartments. We reviewed the bioremediation capacity and mechanisms of Rhodococcus spp. in the treatment of polycyclic aromatic hydrocarbons, phenolic substances, emerging contaminants, heavy metals, and dyes given their human health risks and environmental concern. Different bioremediation techniques were discussed, including experimental conditions, treatment efficiencies, mechanisms, and degradation pathways. The use of Rhodococcus strains in the bioremediation of several compounds is a promising approach due to their features, primarily the presence of appropriate enzyme systems, which result in high decontamination efficiencies; but that vary according to experimental conditions. Besides, the genus Rhodococcus contains a small number of opportunistic species and pathogens, representing an advantage from the point of view of safety. Advances in analytical detection techniques and Molecular Biology have been collaborating to improve the understanding of the mechanisms and pathways involved in bioremediation processes. In the context of using Rhodococcus spp. as bioremediation agents, there is a need for more studies that 1) evaluate the role of these actinomycetes on a pilot and field scale; 2) use genetic engineering tools and consortia with other microorganisms to improve the bioremediation efficiency; and 3) isolate new Rhodococcus strains from environments with extreme and/or contaminated conditions aiming to explore their adaptive capabilities for bioremediation purposes.

Biodegradation of cyanide to ammonia and carbon dioxide by an industrially valuable enzyme from the newly isolated Enterobacter zs

The biodetoxification of cyanide-rich wastewater has been suggested as an appropriate technique due to its environmental friendliness and cost effectiveness. In this research, Enterobacter zs that was newly isolated from cyanide-polluted wastewater was selected to catalyze cyanide via an enzymatic mechanism. Enzyme was purified and its activity was also determined by ammonia assay. Subsequently, the operational procedure was optimized to enhance cyanide biodegradation at variable pH values, temperatures and cyanide concentrations using response surface methodology (RSM). The results revealed that the interactions between pH and temperature, as well as those between pH and cyanide concentration, were significant, and the concentration of cyanide in a 650 mg.L^-1 solution was decreased by 73%. According to this study, it can be proposed that due to its higher activity level compared with those of similar enzymes, this enzyme can prove useful in enzymatic biodegradation of cyanide which is a promising approach in the treatment of industrial effluent.

Enhanced cyanide biodegradation by immobilized crude extract of Rhodococcus UKMP-5M

The capability of the crude extract of Rhodococcus UKMP-5M was enhanced by adopting the technology of immobilization. Among the matrices screened to encapsulate the crude extract, gellan gum emerged as the most suitable immobilization material, exceeding the activity of cyanide-degrading enzyme by 61% and 361% in comparison to alginate carrier and non-immobilized crude extract, respectively. Improved bead mechanical strength which supported higher biocatalyst activity by 63% was observed when concentration of gellan gum, concentration of calcium chloride, number of beads and bead size were optimized. The immobilized crude extract demonstrated higher tolerance towards broad range of pH (5-10) and temperature (30°C-40°C), superior cyanide-degrading activity over time and improved storage stability by maintaining 76% of its initial activity after 30 days at 4°C. Furthermore, repeated use of the gellan gum beads up to 20 batches without substantial loss in the catalytic activity was documented in the present study, indicating that the durability of the beads and the stability of the enzyme are both above adequate. Collectively, the findings reported here revealed that the utilization of the encapsulated crude extract of Rhodococcus UKMP-5M can be considered as a novel attempt to develop an environmentally favourable and financially viable method in cyanide biodegradation.

A novel strategy for the efficient removal of toxic cyanate by the combinatorial use of recombinant enzymes immobilized on aminosilane modified magnetic nanoparticles

Cyanase detoxifies cyanate by transforming it to ammonia and carbon dioxide in a bicarbonate-dependent reaction, however, dependence on bicarbonate limits its utilization in large-scale applications. A novel strategy was therefore developed for overcoming this bottleneck by the combined application of cyanase (rTl-Cyn) and carbonic anhydrase (rTl-CA). The synergistic effect of rTl-Cyn and rTl-CA could reduce the dependence of bicarbonate by 80%, compared to using rTl-Cyn alone. Complete degradation of cyanate (4 mM) was achieved with buffered conditions and 85 ± 5% degradation with industrial wastewater sample, when 20 U of rTl-Cyn was applied. Furthermore, a similar percentage of degradation was achieved using 80% less bicarbonate, when rTl-Cyn and rTl-CA were used together under identical conditions. In addition, rTl-Cyn and rTl-CA were immobilized onto the magnetic nanoparticles and their catalytic activity, stability and reusability were also evaluated. This is the first report on the synergistic biocatalysis by rTl-Cyn and rTl-CA, for cyanate detoxification.

Significant increase in cyanide degradation by Bacillus sp. M01 PTCC 1908 with response surface methodology optimization

Cyanide is used in many industries despite its toxicity. Cyanide biodegradation is affordable and eco-friendly. Sampling from cyanide-contaminated areas from the Muteh gold mine and isolation of 24 bacteria were performed successfully. The selected bacteria-'Bacillus sp. M01'-showed maximum tolerance (15 mM) to cyanide and deposited in Persian Type Culture Collection by PTCC No.: 1908. In the primary experiments, effective factors were identified through the Plackett-Burman design. In order to attain the maximum degradation by Bacillus sp. M01 PTCC 1908, culture conditions were optimized by using response surface methodology. By optimizing the effective factor values and considering the interaction between them, the culture conditions were optimized. The degradation percentage was calculated using one-way ANOVA vs t test, and was found to have increased 2.35 times compared to pre-optimization. In all of the experiments, R² was as high as 91%. The results of this study are strongly significant for cyanide biodegradation. This method enables the bacteria to degrade 86% of 10 mM cyanide in 48 h. This process has been patented in Iranian Intellectual Property Centre under Licence No: 90533.

Expression of a novel recombinant cyanate hydratase (rTl-Cyn) in Pichia pastoris, characteristics and applicability in the detoxification of cyanate

A recombinant Pichia pastoris harbouring the cyanate hydratase gene (rTl-Cyn) from the thermophilic fungus Thermomyces lanuginosus SSBP yielded a high titre of extracellular cyanate hydratase (100±13UmL^-1) which was ∼10-fold higher than the native fungal strain. The purified rTl-Cyn had a molecular mass of ∼20kDa on SDS-PAGE, with K_m, V_max, k_cat and k_cat/K_m values of 0.34mM, 2857.14µmolesmg^-1min^-1, 2.14×10⁴s^-1 and 6.3 ×10⁷M^-1s^-1, respectively. Its properties of thermostability, pH stability, and heavy metals insensitivity, make it a suitable candidate for bioremediation in extreme environments. The rTl-Cyn was able to degrade toxic cyanate completely with the liberation of ammonia, which was confirmed by FTIR analysis. This is the first report of any known cyanate hydratase that has been expressed in P. pastoris, characterized and effectively evaluated for cyanate detoxification.