Biodegradation of phorate in soil and rhizosphere of Brassica juncea (L.) (Indian Mustard) by a microbial consortium Radha Rani * , Asha Juwarkar Environmental Biotechnology Division, National Environmental Engineering Research Institute, Nehru Marg, Nagpur, Maharashtra 440020, India article info Article history: Received 30 March 2012 Received in revised form 10 April 2012 Accepted 10 April 2012 Available online 9 May 2012 Keywords: Phorate Biodegradation Brassica juncea Rhizosphere Soil Microbial consortium abstract The investigation was carried out to assess the potential of bacterial isolates to degrade phorate in soil and to study the effect of presence of plants, Brassica juncea, on the biodegradation process. The bacterial consortium consisting of three isolates viz. Ralstonia eutropha, Pseudomonas aeruginosa and Enterobacter cloacae obtained by enrichment on phorate could degrade it up to 73  3% in aqueous medium and 55  4% in a sandy loam soil. The degradation of phorate by the consortium in the soil was increased up to 64  5% in the presence of B. juncea. Biodegradation of phorate in soil in presence of plants alone was 38  4% as compared to 15  2% in controls. Additionally, all the three isolates were found to possess plant growth promoting potential. Thus, the isolates can be used for remediation of sites contaminated with phorate and other organophosphates. B. juncea may be a potential plant for phytoremediation and rhizoremediation of such sites. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Phorate {O,O-diethyl S-[(ethylthio)methyl]phosphorodithioate} is one of the most toxic organophosphorous insecticide extensively used in agriculture, ornamental plants and forests to control sucking and chewing insects. In India the total production of phorate is estimated to be 48 hundred thousand kg (Bano and Musarrat, 2003) and according to the environment protection agency (EPA), about 1 million kg of phorate, active compound, was used in US alone in 1999 (EPA Crop life America Annual Survey, 1999). The World Health Organisation (WHO) classifies phorate as an extremely hazardous pesticide; also the Food and Agriculture Organization has banned its usage in the developing countries, hence its continuous use is a growing concern. In order to remediate the soils contaminated with phorate, their biodegradation using bacteria and/or enzymes has been suggested to be one of the effective measures. Also, phytoremediation has emerged as a promising technique for environmental cleanup, which offers the advantage of being quite a novel, cost effective and sustainable technology for remediation of sites contaminated with pesticides (McCutcheon and Schnoor, 2003). During rhizor- emediation, microbial biodegradation of pollutants is enhanced in the rhizosphere due to the release of plant metabolites (Kuiper et al., 2004). Though, phytoremediation and rhizoremediation of pesticides and other pollutants is often reported (Daane et al., 2001; Shaw and Burns, 2004), their applicability at field level is seldom. In the present investigation, attempts were made to isolate and characterize soil bacteria capable of phorate degradation. Four different plant species viz. Mimosa pudica, Medicago sativa, Brassica juncea and Pisum sativum, were evaluated for their tolerance towards phorate at three different phorate concentrations (5, 10 and 20 mg kg 1 ). Among them B. juncea was found to be most tolerant to phorate at all the phorate concentrations (unpublished). Thus, it was selected for further studies. Degradation of phorate in soil, in the presence of bacterial isolates alone and in combination of B. juncea was studied. The study was planned to assess the potential of bacterial isolates to degrade phorate in soil and to investigate the effect of presence of plants (B. juncea) on phorate biodegradation by the isolates. 2. Materials and methods Analytical grade phorate obtained from Dr. Ehrenstorfer GmbH (Germany) was used as a standard. Technical grade phorate, purity, >95% was provided by Meerut agrochemicals limited, India. All the chemicals and solvents used were of AR and GC grade respectively. * Corresponding author. Tel.: þ91 9823434025; fax: þ91 0712 2222725. E-mail address: raadharaani1982@gmail.com (R. Rani). Contents lists available at SciVerse ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod 0964-8305/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ibiod.2012.04.004 International Biodeterioration & Biodegradation 71 (2012) 36e42