Biological Remediation of Cyanide: A Review

Cyanide and its complexes are produced by industries all over the world as waste or effluents. Biodegradation is considered to be the cheapest and the most effective method to get rid of cyanide in the environment. Several studies on different types of microorganisms that can degrade cyanide in the environment have been carried out. Hydrolytic, oxidative, reductive, and substitutive/transfer reactions are some of the common pathways used by microorganisms in cyanide degradation. Biodegradation of cyanide can occur aerobically or an-aerobically depending on the environmental conditions. Immobilised enzymes or microorganisms prove to be very effective method of degradation. Microorganisms such as Klebsiella oxytoca, Corynebacterium nitrophilous, Brevibacterium nitrophilous, Bacillus spp., Pseudomonas spp. and Rhodococcus UKMP-5M have been reported to be very effective in biodegradation of cyanide

Batch growth kinetic studies of locally isolated cyanide-degrading Serratia marcescens strain AQ07

The evaluation of degradation and growth kinetics of Serratia marcescens strain AQ07 was carried out using three half-order models at all the initial concentrations of cyanide with the values of regression exceeding 0.97. The presence of varying cyanide concentrations reveals that the growth and degradation of bacteria were affected by the increase in cyanide concentration with a total halt at 700 ppm KCN after 72 h incubation. In this study, specific growth and degradation rates were found to trail the substrate inhibition kinetics. These two rates fitted well to the kinetic models of Teissier, Luong, Aiba and Heldane, while the performance of Monod model was found to be unsatisfactory. These models were used to clarify the substrate inhibition on the bacteria growth. The analyses of these models have shown that Luong model has fitted the experimental data with the highest coefficient of determination (R2) value of 0.9794 and 0.9582 with the lowest root mean square error (RMSE) value of 0.000204 and 0.001, respectively, for the specific rate of degradation and growth. It is the only model that illustrates the maximum substrate concentration (Sm) of 713.4 and empirical constant (n) of 1.516. Tessier and Aiba fitted the experimental data with a R2 value of 0.8002 and 0.7661 with low RMSE of 0.0006, respectively, for specific biodegradation rate, while having a R2 value of 0.9 and RMSE of 0.001, respectively, for specific growth rate. Haldane has the lowest R2 value of 0.67 and 0.78 for specific biodegradation and growth rate with RMSE of 0.0006 and 0.002, respectively. This indicates the level of the bacteria stability in varying concentrations of cyanide and the maximum cyanide concentration it can tolerate within a specific time period. The biokinetic constant predicted from this model demonstrates a good ability of the locally isolated bacteria in cyanide remediation in industrial effluents. © 2017, Springer-Verlag GmbH Germany, part of Springer Nature

Mathematical modelling of molybdenum reduction to Mo-blue by a cyanide-degrading bacterium

Molybdenum, an emerging pollutant, has being demonstrated recently to be toxic to spermatogenesis in several animal model systems. Metal mines especially gold mine often use cyanide and hence isolation of metal-reducing and cyanide-degrading bacteria can be useful for the bioremediation of these pollutants. Preliminary screening shows that three cyanide-degrading bacteria were able to reduce molybdenum to molybdenum blue (Mo-blue) when grown on a molybdate low phosphate minimal salts media. Phylogenetic analyses of the 16S rRNA gene of the best reducer indicates that it belongs to the Serratia genus. A variety of mathematical models such as logistic, Gompertz, Richards, Schnute, Baranyi-Roberts, von Bertalanffy, Buchanan three-phase and Huang were used to model molybdenum reduction, and the best model based on statistical analysis was modified Gompertz with lowest values for RMSE and AICc, highest adjusted R2 values, with Bias Factor and Accuracy Factor nearest to unity (1.0). The reduction constants obtained from the model will be used to carry out secondary modelling to study the effect of various parameters such as substrate, pH and temperature to molybdenum reduction

Optimisation of biodegradation conditions for cyanide removal by Serratia marcescens strain AQ07 using one-factor-at-a-time technique and response surface methodology behavior

Gold mining companies are known to use cyanide to extract gold from minerals. The indiscriminate use of cyanide presents a major environmental issue. Serratia marcescens strain AQ07 was found to have cyanidedegrading ability. Optimisation of biodegradation condition was carried out utilising one factor at a time and response surface methodology. Cyanide degradation corresponded with growth rate with a maximum growth rate of 16.14 log cfu/mL on day 3 of incubation. Glucose and yeast extract are suitable carbon and nitrogen sources. Six parameters including carbon and nitrogen sources, pH, temperature, inoculum size and cyanide concentration were optimised. In line with the central composite design of response surface methodology, cyanide degradation was optimum at glucose concentration 5.5 g/L, yeast extract 0.55 g/L, pH 6, temperature 32.5 �C, inoculum size 20 % and cyanide concentration 200 mg/L. It was able to stand cyanide toxicity of up to 700 mg/L, which makes it an important candidate for bioremediation of cyanide. The bacterium was observed to degrade 95.6 % of 200 mg/L KCN under the optimised condition. Bacteria are reported to degrade cyanide into ammonia, formamide or formate and carbon dioxide, which are less toxic by-products. These bacteria illustrate good cyanide degradation potential that can be harnessed in cyanide remediation

Biodegradation of cyanide by cyanide dihydratase from locally isolated Serratia marcescens isolate AQ07

Cyanide is a very toxic chemical and is one of the environmental pollutants found in sewage. Serratia marcescens isolated from soil sample around Universiti Putra Malaysia (3˚00’23.91"N, 101˚42’31.45"E) was found to have cyanide degrading capability. Spectrophotometric method was used to examine the biodegradation ability of the bacteria in free and immobilised forms using cyanide incorporated buffer medium. Factors affecting cyanide biodegradation such as carbon and nitrogen sources, pH of medium, inoculums size, cyanide concentration and temperature were optimised using one factor at time and response surface methods. Cyanide tolerance and effect of heavy metals (silver, arsenic, cadmium, cobalt, chromium, copper, mercury, nickel, lead and zinc) were investigated. The results illustrates that glucose at 5.5 g/L, yeast extract at 0.55 g/L, pH 6, 20% inoculums size, 200 mg/L cyanide concentration and 32.5ºC are the optimum biodegradation conditions required by the bacteria. Immobilised form of the bacteria showed better biodegradation in terms of duration as it degrades the cyanide in 24 hours compared to free cells that require 72 hours degradation process. The bacteria can tolerate 700 mg/L cyanide concentration in free cells and 900 mg/L in immobilised forms. Heavy metals tested at 1 ppm illustrates that the bacteria could stand their effect with the exception of mercury, which degraded only 24.7% in free cells and 61.6% in immobilised forms. Enzyme activity assay illustrates that the bacteria follow the hydrolytic pathway catalysed by cyanide dihydratase to degrade the cyanide. The purified enzyme was able to detoxify 82% of 2 mM potassium cyanide in 10 min of incubation and the rate of cyanide depletion improved linearly as the enzyme concentration is increased. Hydrolysis of cyanide by the purified enzyme fits Michaelis-Menten saturation kinetics when examined over cyanide concentration of 5 mM potassium cyanide. Lineweaver-Burk plot revealed a linear response at 5 mM KCN and less. Michaelis-Menten constant (Km) for best-fit values of 26.52 and Vmax value of 1.13 and R2 value of 0.9 were determined. Total enzyme activity for crude extract stands at 79.9 and 49, 880 mg/L total protein. After final purification process, the total enzyme activity stands at 0.165 with a total protein of 52 mg/L demonstrating yield of 0.207% and purification fold of 65.78. Effect of pH and temperature revealed that enzyme activity was most active at pH of 8 and temperature of 27ºC. The temperature stability test carried out on the enzyme illustrated that it was stable for 70 days at – 20ºC and when stored at 4ºC, the stability starts reducing after 4 days of incubation. Furthermore, SDS-PAGE electrophoresis post purification revealed the molecular weight of the enzyme to be ~38 kDa, which is a further affirmation. Serratia marcescens isolate AQ07 was observed to have the ability to degrade cyanide. Suitable growth and biodegradation conditions were obtained using the optimisation methods. It demonstrates that immobilised cells of the bacteria have a greater ability for cyanide biodegradation compared to free cells, which can be applied for cyanide treatment in sewage. It has been registered in the gene bank as isolate AQ07 with assigned accession number KP21329

Optimisation of biodegradation conditions for cyanide removal by Serratia marcescens strain AQ07 using one-factor-at-a-time technique and response surface methodology

Gold mining companies are known to use cyanide to extract gold from minerals. The indiscriminate use of cyanide presents a major environmental issue. Serratia marcescens strain AQ07 was found to have cyanide-degrading ability. Optimisation of biodegradation condition was carried out utilising one factor at a time and response surface methodology. Cyanide degradation corresponded with growth rate with a maximum growth rate of 16.14 log cfu/mL on day 3 of incubation. Glucose and yeast extract are suitable carbon and nitrogen sources. Six parameters including carbon and nitrogen sources, pH, temperature, inoculum size and cyanide concentration were optimised. In line with the central composite design of response surface methodology, cyanide degradation was optimum at glucose concentration 5.5 g/L, yeast extract 0.55 g/L, pH 6, temperature 32.5 °C, inoculum size 20 % and cyanide concentration 200 mg/L. It was able to stand cyanide toxicity of up to 700 mg/L, which makes it an important candidate for bioremediation of cyanide. The bacterium was observed to degrade 95.6 % of 200 mg/L KCN under the optimised condition. Bacteria are reported to degrade cyanide into ammonia, formamide or formate and carbon dioxide, which are less toxic by-products. These bacteria illustrate good cyanide degradation potential that can be harnessed in cyanide remediation

Optimisation of biodegradation conditions for cyanide removal by Serratia marcescens strain AQ07 using one-factor-at-a-time technique and response surface methodology

Gold mining companies are known to use cyanide to extract gold from minerals. The indiscriminate use of cyanide presents a major environmental issue. Serratia marcescens strain AQ07 was found to have cyanide-degrading ability. Optimisation of biodegradation condition was carried out utilising one factor at a time and response surface methodology. Cyanide degradation corresponded with growth rate with a maximum growth rate of 16.14 log cfu/mL on day 3 of incubation. Glucose and yeast extract are suitable carbon and nitrogen sources. Six parameters including carbon and nitrogen sources, pH, temperature, inoculum size and cyanide concentration were optimised. In line with the central composite design of response surface methodology, cyanide degradation was optimum at glucose concentration 5.5 g/L, yeast extract 0.55 g/L, pH 6, temperature 32.5 °C, inoculum size 20 % and cyanide concentration 200 mg/L. It was able to stand cyanide toxicity of up to 700 mg/L, which makes it an important candidate for bioremediation of cyanide. The bacterium was observed to degrade 95.6 % of 200 mg/L KCN under the optimised condition. Bacteria are reported to degrade cyanide into ammonia, formamide or formate and carbon dioxide, which are less toxic by-products. These bacteria illustrate good cyanide degradation potential that can be harnessed in cyanide remediation