Journal of Hazardous Materials 190 (2011) 351–358 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Decolorization of sulfonated azo dye Metanil Yellow by newly isolated bacterial strains: Bacillus sp. strain AK1 and Lysinibacillus sp. strain AK2 O. Anjaneya a , S. Yogesh Souche b , M. Santoshkumar a , T.B. Karegoudar a,∗ a Department of Biochemistry, Gulbarga University, Gulbarga - 585106, Karnataka, India b National Centre for Cell Science, Ganeshkhindi, Pune - 411007, India article info Article history: Received 3 December 2010 Received in revised form 8 February 2011 Accepted 14 March 2011 Available online 21 March 2011 Keywords: Decolorization Azo dyes Bacillus sp. AK1 Lysinibacillus sp. AK2 Azoreductase Phytotoxicity abstract Two different bacterial strains capable of decolorizing a highly water soluble azo dye Metanil Yellow were isolated from dye contaminated soil sample collected from Atul Dyeing Industry, Bellary, India. The individual bacterial strains Bacillus sp. AK1 and Lysinibacillus sp. AK2 decolorized Metanil Yellow (200 mg L -1 ) completely within 27 and 12 h respectively. Various parameters like pH, temperature, NaCl and initial dye concentrations were optimized to develop an economically feasible decolorization process. The maximum concentration of Metanil Yellow (1000 mg L -1 ) was decolorized by strains AK2 and AK1 within 78 and 84 h respectively. These strains could decolorize Metanil Yellow over a broad pH range 5.5–9.0; the optimum pH was 7.2. The decolorization of Metanil Yellow was most efficient at 40 ◦ C and confirmed by UV–visible spectroscopy, TLC, HPLC and GC/MS analysis. Further, both the strains showed the involvement of azoreductase in the decolorization process. Phytotoxicity studies of catabolic products of Metanil Yellow on the seeds of chick pea and pigeon pea revealed much reduction in the toxicity of metabolites as compared to the parent dye. These results indicating the effectiveness of strains AK1 and AK2 for the treatment of textile effluents containing azo dyes. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Azo dyes constitute the largest class of dyes with the great- est variety of colors, having wide applications in textile, food, printing and cosmetic industries [1]. Azo dyes are characterized by the presence of one or more azo bonds –N N–, which are responsible for their coloration. When such a bond is broken the compound loses its color [2]. The annual world wide production of azo dyes was estimated to be around one million tons and more than 10,000 structurally different azo dyes are currently in use [3,4]. It is reported that about 300,000 tons of different dyestuffs are used per year for textile dyeing operations. Thus the dyestuff, textile, paper, and leather industries are the major consumers of synthetic azo dyes and produce effluents that are usually resistant to the physico-chemical treatments and consequently served as the major source of water pollution. It is estimated that 10–15% of the total dye consumed in dyeing processes may be found in wastew- ater. This led to severe contamination of both surface and ground water [5,6]. Unless the wastewater is properly treated, these dyes may significantly affect the photosynthetic activity of aquatic life due to reduced light penetration as well as toxic to some aquatic life [7]. ∗ Corresponding author. Tel.: +91 8472 263289; fax: +91 8472 245632. E-mail address: goudartbk@rediffmail.com (T.B. Karegoudar). Metanil Yellow (Acid Yellow 36) is a highly water-soluble dye is extensively used for the coloring of soap, spirit lacquer, shoe pol- ish, bloom sheep dip, for the preparation of wood stains, dyeing of leather, manufacture of pigment lakes and for staining paper [8]. Though Metanil Yellow is a non-permitted colorant, but still it is widely used as a colorant in sweet meat, ice creams, soft drinks and beverages. Due to its orange-yellow color, the dye is also exten- sively used for coating turmeric. The dye is highly suitable for the preparation of colored water-fast inks [9]. Toxicity data reveals that oral feeding or intraperitoneal and intratesticular administration of Metanil Yellow in animals pro- duces testicular lesions due to which seminiferous tubules suffer damage and results in the decreased rate of spermatogenesis [10]. Studies have shown that 13.6% of the orally administered dose of Metanil Yellow (15 mg 200 g -1 rat) is retained even after 96 h in the gastrointestinal tract, which may be responsi- ble for decreased mucin secretion from the intestinal mucous cells [11]. On oral consumption, it causes toxic methaemoglobi- naemia [12] and cyanosis [13] in humans, while skin contact results into allergic dermatitis [14]. Metanil Yellow also has tumour-producing effects and can create intestinal and enzymic disorders in human body [11]. Though it is not mutagenic but can alter the expression of genes [15]. Thus, keeping the haz- ardous effects of this dye in view, attempts have been made by various researchers to remove Metanil Yellow from wastewater [10,16,17]. 0304-3894/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2011.03.044