Biodegradation of cyanide using Serratia sp. isolated from contaminated soil of gold mine in Takab

Introduction : Cyanide is a toxic and hazardous compound for all organisms which is produced enormously by human being and causes the environment pollution. Biodegradation is the best method for cyanide elimination in industrial wastewater. The aims of this study were isolation of cyanide degrading bacteria from contaminated soil and investigation of their ability for cyanide degradation.   Materials and methods: After soil samples collection, enrichment of cyanide degrading bacteria was performed in a minimal medium containing 0.5 mM potassium cyanide. The ability of isolated bacterium to utilize the cyanide as sole carbon and nitrogen source was investigated. Cyanide degradation and ammonium production was determined in growth medium using picric acid and Nessler’s regent methods. Toxicity effect of different cyanide compounds on bacterial growth was determined using minimum inhibitory concentration. In addition, the ability of the isolated bacterium to utilize different cyanide compounds was investigated . Identification of the isolate was undertaken using morphological, physiological and biochemical characteristics and molecular analysis .   Results : A bacterium with ability to degrade cyanide as sole carbon and nitrogen source was isolated from soil. This bacterium named as isolate MF1. MF1 degraded cyanide in growth medium in alkaline condition after 40 hours. Moreover this isolate tolerated more than 7 mM potassium cyanide. The results showed that there was a direct relation between decreasing of cyanide concentration, increasing of ammonia concentration and growth of MF1. In addition, the isolated bacterium demonstrated the ability to utilize different cyanide compounds as sole carbon and nitrogen source. The results of morphological and physiological characteristics showed that this bacterium belonged to the Serratia sp. Moreover, 16S rDNA sequencing and phylogenetic analyses exhibited that MF1 strain was similar to Serratia nematodiphila with 99% homology .   Discussion and conclusion : The results demonstrated that the isolated bacterium is a suitable candidate for degradation of cyanide in alkaline condition. This bacterium could introduce for treatment of industrial wastewater and sites that contaminated with cyanide.