Biotransformation of CI Acid Blue 113 and other dyes by Shewanella sp. P6 Sunil Biala, a Priyanka Chauhan, a Bhupinder Singh Chadha, a Bikram Singh b and Harvinder Singh Saini a, * a Department of Microbiology, Guru Nanak Dev University, Amritsar, 143005, India Email: sainihs@yahoo.com b Department of Natural Plant Products, IHBT, Palampur, India Received: 9 October 2012; Accepted: 2 November 2012 The isolate P 6 , an indigenous Shewanella sp., was able to decolorise 90% of CI Acid Blue 113 in just 30 min of incubation under anoxic conditions. The decolorisation potential of cells was not significantly affected even in the presence of 2% (w/v) sodium chloride and 8% (w/v) sodium sulphate. Mass spectrometric analysis detected the formation of aniline sodium salt, 1,4-diaminonaphthalene, 5-amino-8-(phenylamino)-naphtha- lene-1-sulphonic acid sodium salt and 8-(phenylamino)-naphthalene-1-sulphonic acid sodium salt. Further, cells of P 6 decolorised the raw effluent collected from the equalisation tank of a textile industry wastewater treatment plant. The water-soluble dyes/intermediates present in the sludge, generated after chemical flocculation of raw effluent, were transformed by P 6 cells within 24 h of incubation under anoxic conditions. Thus, isolate P 6 has a potential application in the biological treatment of liquid and solid waste of textile processing plants because of its efficient decolorisation and transformation properties. Coloration Technology Society of Dyers and Colourists Introduction Textile dyeing plants are among the major contributors to environmental pollution owing to the release of untreated effluent and the solid waste/sludge generated during chemical treatment of effluent. Approximately 7 9 10 5 t of 10 000 different dyes and pigments is used in dyeing plants worldwide annually. It has been reported that approximately 10–15% of the dye used in dye baths is lost as unreacted dye [1]. The release of such coloured compounds into water bodies is not only aesthetically displeasing but also drastically affects photosynthesis in aquatic ecosystems by blocking the penetration of light [2,3]. Apart from being toxic to flora and fauna, these compounds could cause mutations by binding to DNA, with acute and chronic manifestations in humans [4]. The conventional physical and chemical methods, including adsorption, photodegradation, precipitation, filtration, elec- trolysis and oxidation, although effective for colour removal, do not address the problem of the toxicity of dyes and their intermediates. In addition, these methods have high recurring costs, as a constant supply of adsorbents/ energy is required, and the solid waste generated requires special treatment/disposal methods [5]. Azo dyes, having one or more azo bonds (–N=N–), consti- tute the largest and most versatile class of synthetic dyes, as they are cheap and available in different bright shades. The precursors used for azo dye synthesis and their degradation products formed by chance reduction of the azo bond, especially aromatic amines and nitroaromatics, tend to persist in the environment. Biological treatment of textile plant effluent is an effective and environmentally friendly option, as the concerted metabolic activity of mixed populations could result in the decolorisation and degradation of dyes and their intermediates to environmentally benign products, which would not be possible by other treatment options. The initial investment for setting up a biological treatment process might be higher; however, long-term operations provide treatment efficiency at a lower cost compared with physical/chemical methods employed for effluent treatment [6]. The effective biological treatment of textile industrial effluent needs a sequential anaerobic/anoxic-aerobic system in which the initial anaerobic/anoxic stage reduces the azo bond in the absence of or under low partial pressure of oxygen, and breakdown of the aromatic amines formed is achieved in the aerobic stage. Although there are reports available in the literature regarding the mineralisation of azo dyes by a single bacterial culture under both conditions [7], different microbial inocula for these two stages make the process highly effective [8,9]. The overall success of the process invariably depends on initial breakdown of structur- ally diverse azo dyes under anoxic/aerobic conditions [10]. Among the various azo-dye-degrading bacteria, the members of Shewanella are known for the removal of different classes of dyes by using a wide variety of electron acceptors under anaerobic/anoxic conditions for decolorisation [11,12]. The present paper reports on the isolation of an indig- enous Shewanella sp. P 6 , isolated from the waste disposal site of a dyeing unit, and its extraordinary decolorisation ability under anoxic conditions. The dye CI Acid Blue 113 was used as a model compound owing to its complex structure and its extensive use in cotton and wool dyeing for obtaining a deep shade of navy blue. Experimental Materials CI Acid Blue 113 (AB-113, 97% pure) was purchased from Sigma-Aldrich, USA (Figure 1). The other dyes, such as CI Acid Red 88 (AR-88), CI Acid Red 119 (AR-119), CI Reactive Black 5 (RB-5), CI Reactive Orange 122 (RO-122), CI Reactive Blue 160 (RB-160) and CI Reactive Red 120 (RR- 120), were purchased from the local market and purified by recrystallisation at 20 °C from their saturated solutions in ethanol. The stock solutions of dyes made in distilled water were sterilised using 0.2 lm membrane filters (Pall Life Sciences, USA). The media components and chemicals © 2013 The Authors. Coloration Technology © 2013 Society of Dyers and Colourists, Color. Technol., 129,1–8 1 doi: 10.1111/cote.12045