Journal of Hazardous Materials 262 (2013) 674–684 Contents lists available at ScienceDirect Journal of Hazardous Materials jou rn al hom epage: www.elsevier.com/locate/jhazmat Biotransformation of Direct Blue 1 by a moderately halophilic bacterium Marinobacter sp. strain HBRA and toxicity assessment of degraded metabolites A.S. Arun Prasad a , V.S.V. Satyanarayana b , K.V. Bhaskara Rao a,∗ a Division of Environmental Biotechnology, School of Biosciences and Technology, VIT University, Vellore, India b Chemistry Department, School of Basic Sciences, IIT Mandi, Himachal Pradesh, India h i g h l i g h t s • A moderately halophilic bacterial strain was isolated that effectively degraded DB-1. • HBRA was identified to be Marinobacter sp. • Deduction of possible biotransformation pathway for DB-1. • Toxicity evaluation of DB-1 and its degraded metabolites. a r t i c l e i n f o Article history: Received 28 May 2013 Received in revised form 4 September 2013 Accepted 7 September 2013 Available online xxx Keywords: Direct Blue-1 Marinobacter sp. strain HBRA Biotransformation Toxicity a b s t r a c t The ability of halophiles to survive in the extreme salt concentrations has gained them the importance of being used in the treatment of industrial waste waters. A moderately halophilic bacterial strain with the ability to degrade the complex azo dye Direct Blue-1 (DB-1) was isolated from sea water and identified as Marinobacter sp. strain HBRA. Complete decolorization of DB-1 (100 mg L -1 ) was achieved in 6 h at 37 ◦ C, pH 8 and with 70 g L -1 NaCl. Decolorization was analyzed by UV–vis spectrophotometer. The FT-IR spectrum revealed that Marinobacter sp. strain HBRA specifically targeted azo bond (N N) at 1631 cm -1 to break down Direct Blue-1. Formation of metabolites at different retention times in HPLC indicated degradation. Biotransformation pathway for DB-1 was proposed based on LC–MS. Phytotoxicity study revealed the less toxic nature of the metabolites compared to the dye. Genotoxicity with Allium cepa confirmed the cytotoxic nature of DB-1 by inducing several chromosomal abnormalities compared to the negligible effects of degraded metabolites. The current study is the first report on the detoxification of DB-1 by Marinobacter sp. strain HBRA. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Among the various colourants used in textile industry, azo dyes constitute 70% by weight the most common compounds used for this purpose. Azo dyes are represented by substituted aromatic rings that are joined by one or more azo groups (R 1 N N R 2 ). The azo groups are generally connected to benzene and naph- thalene rings and to aromatic heterocycles, which intensify the colour of the azo compounds and provide bonding affinity groups [1]. The largest amount of azo dyes is used for the dyeing of tex- tiles, of which nearly 10–15% dyestuff remains unbound to the fibre and is therefore released into the environment leading to ∗ Corresponding author at: School of Bio Sciences and Technology, VIT University, Vellore 632 014, Tamil Nadu, India. Tel.: +91 9894350824. E-mail address: kokatibhaskar@yahoo.co.in (K.V. Bhaskara Rao). severe contamination of surface and ground waters [2]. There- fore the treatment of dye wastewaters is necessary before their safe disposal to the environment [3]. Different physicochemical methods such as adsorption, chemical oxidation, coagulation and precipitation are available for the treatment of dye containing effluents [4,5]. High cost, limited versatility, low efficiency and for- mation of secondary sludge which requires additional treatment are the major disadvantages of physicochemical methods. These constraints have led to the consideration of biological methods as attractive options as they are cost effective, environmental friendly, produce less sludge and are efficient in completely mineralizing organic pollutants [6]. Microorganisms play a remarkable role in decomposition and ultimate mineralization of various azo dyes [7–9]. Bacterial decolorization of azo dyes has gained importance in recent times [10] as they are easy to culture and grow quickly. Many microorganisms from various taxonomic groups have been found to decolorize different kinds of azo dyes [11–15]. These conventional 0304-3894/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2013.09.011