Biological degradation of cyanide compounds

doi:10.1016/j.copbio.2004.03.006

Current Opinion in Biotechnology

Volume 15, Issue 3, June 2004, Pages 231-236

https://doi.org/10.1016/j.copbio.2004.03.006 Get rights and content

Abstract

Cyanide compounds are produced as waste products of a number of industrial processes and several routes for their removal from the environment are under investigation, including the use of biodegradation. The most recent developments in this area have come from studies of the hydrolytic and oxidative pathways for biodegradation and the conditions that affect their activity. The biodegradation of cyanide under anaerobic conditions has also recently demonstrated the feasibility for concomitant biogas generation, a possible economic benefit of the process. Significant advances have been reported in the use of plants for the phytoremediation of cyanide compounds and evidence for the biodegradation of thiocyanate and metal–cyanide complexes has become available. Despite these advances, however, physical and economic factors still limit the application of cyanide biodegradation, as do competing technologies.

Introduction

Cyanide played a principle role in the evolution of life on Earth [1] and remains an important form of nitrogen for microorganisms, fungi and plants. Although some organisms synthesize cyanide, a greater number are capable of cyanide biodegradation. The existence of these pathways has allowed the development of biotechnologies to degrade cyanide compounds in industrial waste streams. Major sources of cyanide discharges include petrochemical refining, the synthesis of organic chemical and plastics, electroplating, aluminum works, the former manufactured gas industry, and metal mining and processing industries. The release of cyanide from these industries has been estimated to be >14 million kg yr⁻¹ [2]. Cyanide can be present in environmental matrices and waste streams as simple cyanides (e.g. HCN, CN⁻, NaCN), metal cyanide complexes, cyanates and nitriles. Degradation pathways are sensitive to the form and concentration of the cyanide compound, the physicochemical conditions of the media, and the presence of interfering and inhibitory compounds. The development of biodegradation strategies for these varied conditions requires a comprehensive understanding of the biological pathways. Presented here are recent studies of these pathways, along with a brief discussion of current advances in the development of cyanide-related biotechnologies. Limiting factors for these biotechnologies are also discussed.

Section snippets

Biodegradation of free cyanide and nitriles

There are four general pathways for the biodegradation of cyanide: hydrolytic; oxidative; reductive; and substitution/transfer (Figure 1). Several reviews have described these pathways and the organisms in which they are found 3., 4., 5.. Nevertheless, additional organisms with the capacity for cyanide biodegradation are still being reported 6.•, 7., 8., 9.. More than one pathway can be utilized for cyanide biodegradation in some organisms 3., 10.; the pathway used is dictated by the external

Biodegradation of metal cyanide complexes

Perhaps the greatest need with respect to cyanide biodegradation is biodegradation of metal cyanide complexes. Cyanide can complex with Fe, Au, Cd, Co, Cu and Ni, with the Fe and Au complexes being the most stable. Iron cyanides are the dominant CN species in soil and groundwater [27], with total CN concentrations in contaminated media as high as 4% by weight 28., 29.. As Fe is a ubiquitous element in soils and aquifers, equilibrium favors the formation of complexes such as ferrocyanide [Fe(CN)₆

Recent advances in cyanide biodegradation technologies

Two bioreactor studies with wastewater have renewed the focus on reductive processes (Figure 1) during anaerobic cyanide biodegradation 36., 37.. One advantage of these anaerobic bioreactors is that cyanide biodegradation can support the growth of methanogens, suggesting a possible productive use for biogas generation. Methanogenesis from anaerobic biogranules was inhibited by increasing cyanide concentrations [37], however, so the cyanide concentration in the feedstock may be a limiting

Conclusions

The continued development and application of biotechnologies for cyanide biodegradation is limited primarily by physical and economic factors. Most organisms capable of biodegrading cyanide are sensitive to cyanide concentration, with biodegradation and/or growth rate decreasing above specific thresholds for each organism. Solutions containing cyanide concentrations of up to 100 mg L⁻¹ can be treated, although a commercially marketed strain of Fusarium displaying high levels of cyanide hydratase

Update

Bacterial strains from the genus Klebsiella have been shown to degrade both cyanide and thiocyanate. Strains of Klebsiella oxytoca isolated from cyanide-enriched industrial wastewaters grew on cyanide as the sole nitrogen source [42]. In the presence of cyanide, resting cell cultures produced methane and showed increased activity of nitrogenase, suggesting a reductive pathway for cyanide biodegradation. However, while no formate or formamide were detected in the cell cultures following cyanide

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

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of special interest
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of outstanding interest

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Biological degradation of cyanide compounds

Abstract

Introduction

Section snippets

Biodegradation of free cyanide and nitriles

Biodegradation of metal cyanide complexes

Recent advances in cyanide biodegradation technologies

Conclusions

Update

References and recommended reading

Adv Microb Physiol

FEMS Microbiol Lett

FEMS Microbiol Lett

Lett Appl Microbiol

Process Biochem

Umwelt Schad Forsch

Appl Biochem Biotechnol

Environ Technol

Microbes and microbial enzymes for cyanide degradation

Biodegradation

Biological cyanide destruction mediated by microorganisms

World J Microbiol Biotechnol

Characterisation of a cyanide hydratase gene in the phytopathenogenic fungus Leptosphaeria maculans

Mol Gen Genet

Degradation of the metal-cyano complex tetracyanonickelate (II) by Fusarium oxysporum N-10

Appl Biochem Microbiol

Isolation and characterization of a cyanide-utilizing Burkholderia cepacia strain

World J Microbiol Biotechnol

Cyanide catabolizing enzymes in Trichoderma spp

Enzyme Microb Technol

Chemical and biological removal of cyanides from aqueous and soil-containing systems

Appl Biochem Microbiol

Substrate-regulated cyanide hydratase (chy) gene expression in Fusarium solani: the potential of a transcription-based assay for monitoring the biotransformation of cyanide complexes

Environ Microbiol

The nitrilase family of CN hydrolysing enzymes – a comparative study

J Appl Microbiol

The cyanide hydratase enzyme of Fusarium lateritium has nitrilase activity

FEMS Microbiol Lett

Metabolism of benzonitrile by Cryptococcus sp. UFMG-Y28

J Basic Microbiol