Application Potential of Cyanide Hydratase from Exidia glandulosa: Free Cyanide Removal from Simulated Industrial Effluents

Anastasia Sedova,Miroslav Pátek,Barbora Křístková,Ludmila Martínková,Michaela Glozlová,Pavla Bojarová,Petr Novotný,Lenka Rucká

doi:10.3390/catal11111410

Abstract

Industries such as mining, cokemaking, (petro)chemical and electroplating produce effluents that contain free cyanide (fCN = HCN + CN−). Currently, fCN is mainly removed by (physico)chemical methods or by biotreatment with activated sludge. Cyanide hydratases (CynHs) (EC 4.2.1.66), which convert fCN to the much less toxic formamide, have been considered for a mild approach to wastewater decyanation. However, few data are available to evaluate the application potential of CynHs. In this study, we used a new CynH from Exidia glandulosa (protein KZV92691.1 designated NitEg by us), which was overproduced in Escherichia coli. The purified NitEg was highly active for fCN with 784 U/mg protein, kcat 927/s and kcat/KM 42/s/mM. It exhibited optimal activities at pH approximately 6–9 and 40–45 °C. It was quite stable in this pH range, and retained approximately 40% activity at 37 °C after 1 day. Silver and copper ions (1 mM) decreased its activity by 30–40%. The removal of 98–100% fCN was achieved for 0.6–100 mM fCN. Moreover, thiocyanate, sulfide, ammonia or phenol added in amounts typical of industrial effluents did not significantly reduce the fCN conversion, while electroplating effluents may need to be diluted due to high fCN and metal content. The ease of preparation of NitEg, its high specific activity, robustness and long shelf life make it a promising biocatalyst for the detoxification of fCN.

Highlights

Cyanide is widely used in industry due to its chelating and electrolytic properties.For example, it is used to leach gold and silver from their ores
NitEg was produced in E. coli following the general protocol we developed for the production of nitrilases (EC 3.5.5.1) and the related Cyanide hydratases (CynHs) [31]
CynH from the Basidiomycota division, in free cyanide (fCN) solutions of up to 100 mM concentrations at alkaline conditions. This CynH was studied as a potential biocatalyst using model mixtures prepared according to the literature

Summary

Introduction

Cyanide is widely used in industry due to its chelating and electrolytic properties. It is used to leach gold and silver from their ores. These processes generate significant amounts of cyanide waste [1,2]. Cyanide occurs as free cyanide (fCN), i.e., CN− and HCN, or as metal complexes. FCN is the most toxic; at pH ≤8.5, it occurs predominantly as volatile HCN, which is very hazardous [1]. The above industrial effluents contain other chemicals such as sulfide, thiocyanate, ammonia, phenols or metals [4,5,6,7,8,9], which can complicate their treatment

Objectives

Methods

Results

Discussion

Conclusion