BIOTROPIA Vol. 22 No. 2, 2015: 151 - 163 DOI:10.11598/btb.2015.22.2.393 BIOLOGICAL REMEDIATION OF CYANIDE: A REVIEW KARAMBA KABIRU IBRAHIM, MOHD ARIF SYED, MOHD YUNUS SHUKOR and SITI AQLIMA AHMAD* Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia Received 8 April 2014/Accepted 9 November 2015 ABSTRACT 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 clean-up cyanide from 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 anaerobically depending on the environmental conditions. Immobilized 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. Keywords: biodegradation, cyanide, environment, microorganisms INTRODUCTION reported to have high capital cost but low operating cost. Therefore, these methods are Carbon and nitrogen elements form cyanide. more profitable than the traditional process. They are ubiquitously found in the environment. Biological process that could satiate the need for Amygdalin, which is found in vegetables, fruits, extraction and environmental control is now seeds, cashew nuts, cherries, apricots and bean practiced in some countries that understood the sprouts is a natural source of hydrogen cyanide process (Dash et al. 2009). (HCN) (Mark et al. 1999). Chemical treatment is the most widely used method in the degradation Cyanide Degrading Microorganisms of industrial effluents containing cyanide. But, Biological treatment process facilitates growth this treatment is very expensive and sometimes of microorganisms that are essential for inefficient in the process and thus requires an treatment (Akcil 2003). It has been discovered alternative means of treatment (Patil & Paknikar that cyanide naturally occurs in the environment 2000). Researches on microorganisms have been via the degradation of plant cyanogenic carried out to see if they can be an alternative glycosides. A lot of microorganisms are able to means of cyanide degradation. Bioremoval has detoxify simple forms of cyanide (Gadd 2001). been reported to be less expensive than physical Pseudomonas fluorescens NCIMB 11764 has been and chemical methods of cyanide degradation reported to be able to utilize potassium cyanide and faster than natural oxidation (Ozel et al. 2010; (KCN) in fed-batch culture (Kunz et al. 1998). Dash et al. 2009). Destruction of cyanide in Pseudomonas fluorescence has also been reported to wastewaters and tailing solutions by capable degrade ferrocyanide (Arzu & Zumriye 2000). microorganisms has been proved to be an The growth of Pseudomonas fluorescens NCIMB alternative to the long-practiced chemical 11764 on medium containing potassium cyanide methods for the removal of cyanide. Biological (KCN) has also been reported (Kunz et al. 1998). methods of treating industrial effluents have been Cyanide degradation by E scherichia coli, Alcaligenes, * Corresponding author : aqlima@ upm.edu.my 151 BIOTROPIA Vol. 22 No. 2, 2015 Acinetobacter and Bacillus species have also been bioavailability and solubility in the soil water reported in a number of studies. system (Aronstein et al. 1994). It has been reported that strains of bacteria from genus Klebsiella are very effective in the Hydrolytic Reaction bioremediation of cyanide and thiocyanate. K. The following equations show the reactions oxytoca isolated from an industrial waste that occur during hydrolytic pathway for cyanide containing high level of cyanide proliferates well degradation (David et al. 2006): with the cyanide as the only nitrogen source (Kao et al. 2003). It has been reported that K. oxytoca is effective in biodegradation even at concentrations higher than 1 mM of cyanide (Chena et al. 1999). The microorganism biodegrades cyanide to Hydrolytic reactions contain nitriles with R products that are nontoxic using cyanide as the denotes either analiphatic or aromatic group. only nitrogen source aerobically or anaerobically Hydrolytic reactions are catalyzed by cyanide (Kao et al. 2003; Stephen 2004). Seven bacterial hydratase, founding a formamide or cyanidase strains isolated from gold mine environment in and yields formate and ammonia. Cyanide Korea have been found to be very effective in the hydratase is principally a fungal enzyme and is biodegradation of thiocyanate with the initial extremely preserved between species (Barclay et concentration of 150 mg/L within sixteen days of al. 2002). Cyanide dihydratase (cyanidase) is incubation (Lee et al. 2003). Four strains from the produced chiefly by bacteria. Cyanide hydratase genus Bacillus, one strain of Corynebacterium and cyanidase have, in recent times, been nitrophilus and two from Brevibacterium have been presented to have certain resemblances at both found to effectively degrade cyanide. the amino acid and structural stages to nitrilase Pseudomonas pseudoalcaligenes CECT5344 is an and nitrile hydratase enzymes (Reilly & Turner alkaliphilic strain of bacteria that is reported to be 2003). Enzymes that utilize nitrile have been capable of biodegrading cyanide. The organism established in a wide variety of fungal, plant and was isolated from sludge of Guadalquivir bacterial species. Nitrilases and nitrile hydratases (Cordoba, Spain). It proliferates at an optimum modify both aliphatic and aromatic nitriles to the pH of 9.5 and utilizes 2 mM of cyanide as the only equivalent acid or amide, respectively, but indicate hydrogen source (Luque-Almagro et al. 2005 ; less substrate specificity than cyanide hydratase Huertas et al. 2010). The organism can also utilize and cyanide dihydratase. For instance, conversion complex of cyano-metal, cyanate and residue of E . coli with the cyanide hydratase gene from from jewellery industry as the sole nitrogen source Fusarium lateritium permits the proliferation of (Luque-Almagro et al. 2005 ). This strain has been nitriles as the only source of nitrogen. Site- described to possess a cyanide-insensitive directed mutagenesis of this gene stops the respiration system, which includes cytochrome bd- activity of both cyanide hydratase and nitrilase, type alternate oxidase (AOX) that replaces the signifying that cyanide hydratase possesses cytochrome c oxidase (Quesada et al. 2007). nitrilase activity, as well (Nolan et al. 2003). The variety of enzymes in this fantastic family and General Pathway Reaction for Biodegrada- their diverse catalytic act and substrate tion of Free Cyanide specificities grant significant chance for biotechnological improvement, encompassing There are four common pathways involved in the bioremediation of industrial nitrile waste the bioremoval of cyanide i.e. hydrolytic reaction, (Rezende et al. 2000; Dias et al. 2001). oxidative reaction, reductive reaction and substitution/transfer reaction. More than one Oxidative Reaction pathway can be used for cyanide degradation by certain microorganisms (Raybuck 1992; Ezzi- In the oxidative reaction, the cyanate formed Mufaddal & Lynch 2005). The pathway to be used by the enzyme cyanide monoxygenase is changed depends on various factors such as oxygen to ammonia and carbon dioxide by the same availability, pH level of the environment, pathway as cyanate and thiocyanate (David et al. concentrations of the cyanide and cyanide 2006). 152 Biological remediation of cyanide: A review – Ibrahim et al. Substitution/ Transfer Reaction This is referred to as assimilatory pathway. Several genera of bacteria are said to assimilate Cyanide is converted to cyanate by cyanide cyanide. This reaction is more extensively monoxygenase with cyanate standing as the researched in Chromobacterium violaceum. Other catalyst for conversion of cyanate to ammonia and bacteria that utilize this reaction include carbon dioxide dependent on bicarbonate. E scherichia coli, Bacillus megaterium, Citrobacter freundii Cyanases have been identified in several bacteria, and E nterobacter aerogenes (David et al. 2006). The fungi, plants and animals (Guilloton et al. 2002). substitution/transfer reaction uses cyanoalanine The assumed task of cyanase has, for a long time, synthase enzyme as the catalyst using O- been as a defense against poisoning by cyanate acetylserine (OAS) as substrate. (Raybuck 1992). As cyanate is not a familiar metabolite, new essential roles in favor of cyanases in nitrogen and bicarbonate/carbon dioxide metabolism have been suggested. More proposed roles for plant cyanases comprise ammonia absorption as a result of cyanate bioremediation and a task in the concentration and deliverance of The cyanate produced by cyanide + carbon dioxide for photosynthesis (Guilloton et al. monoxygenase is changed to NH4 and CO 2 by 2002). very similar pathway as the cyanate from Another oxidative pathway makes use of thiocyanate (Stephen 2004). cyanide dioxygenase to produce ammonia and carbon dioxide directly (Stephen 2004). Moreover, Thiocyanate Biodegradation in E . coli strain BCN6 and P. fluorescens NCIMB Reactions of cyanide with