INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 3, No 6, 2013 © Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN 0976 – 4402 Received on March 2013 Published on June 2013 1985 In vitro cyanide degradation by Serretia marcescens RL2b Virender Kumar, Vijay Kumar, Tek Chand Bhalla Department of Biotechnology Himachal Pradesh University, Summer Hill Shimla, Himachal Pradesh-171005, India bhallatc@rediffmail.com doi: 10.6088/ijes.2013030600019 ABSTRACT Detoxification of cyanide compounds using biological systems is gaining much attention due to various advantages over the traditional physical and chemical methods. In present study, a cyanide degrading bacterial strain RL2b was isolated from forest soil of Himachal Pradesh. Based on the morphology, physiological, biochemical tests and its 16S rDNA sequence, the bacterial isolate RL2b was identified as Serretia marcescens. In vitro degradation of cyanide by this organism was investigated by varying several cultural conditions viz. medium, carbon and nitrogen sources, pH and temperature. Serretia marcescens RL2b exhibited maximum cyanide degradation in medium M1 containing glycerol and tryptone as carbon and nitrogen source respectively. Cyanide degradation was maximum at pH 6.0 and 35˚C temperature. This bacterial isolate exhibited cyanide tolerance up to 16 mM and highest cyanide degradation at 12 mM in 40 h. The present study revealed that the strain Serretia marcescens RL2b has high cyanide tolerance and degradation potential at wide pH and temperature range and thus has very good potential for efficient cyanide removal from environment. Keywords: Serratia marcescens, cyanide degradation, cyanide tolerance, 16S rDNA sequence 1. Introduction Cyanide is used in the extraction of gold from its ore, electroplating, steel manufacturing, polymer synthesis and dye making. Due to its extensive applications in industries, it is inevitable to use cyanide (Luque-Almargo et al., 2005). Several problems are associated with the discharge of large amounts of cyanide compounds in the environment (Das and Santra, 2011). When cyanide is released in the soil, it may leach through the soil and affects its physical and biological components. Its entry into soil or water system imposes a serious threat to sustainability of the ecosystem (Seepulveda et al., 2010). A number of industrial effluents contain cyanide at a concentration exceeding 100mg/L (Watanabe et al., 1998: Gurbuz et al., 2009). The acceptable limit of cyanide in industrial effluents and polluted environment is 0.2mg/L. Cyanide is toxic to a wide spectrum of organisms because it has the ability to form complexes with metals (Fe 2+ , Mn 2+ and Cu 2+ ) which act as cofactor of many enzymes (Raybuck, 1992: Dumestre et al., 1997). Some microorganisms and plants are capable of metabolizing cyanide due to presence of alternative pathways to utilize or degrade cyanide (Daniel et al., 1994). Microorganisms are able to convert cyanide into other less toxic products like ammonia, formic acid and formamide depending upon the enzyme system they possess (Huertas et al., 2010: Luque-Almargo et al. 2011). The presence of such pathways in biological systems encourages researchers to develop novel processes involving biomaterials for the removal of cyanide from the environment (Kao et al., 2003: Dhillon and Shivaraman, 1999).