Indian Journal of Experimental Biology Vol. 56, November 2018, pp. 820-826 Decolourization of dyes by Alcaligenes faecalis and Bacillus flexus isolated from textile effluent Shikha Saini 1 , Bindu Battan 2 , Rashmi 2 , Shallu Maan 1 & Jitender Sharma 2 * 1 University Institute of Engineering and Technology; Kurukshetra University, Kurukshetra, Haryana, India 2 Department of Biotechnology; Kurukshetra University, Kurukshetra, Haryana, India Received 10 April 2017; revised 10 August 2017 In textile industry, untreated effluents pollute aquatic systems, almost irreversibly. Synthetic dyes not only change the colour of water resources but also make them toxic. In this study, we evaluated decolourizing potential of microbial isolates so as to use them as bioremediation agents. Two bacterial isolates, Bacillus flexus and Alcaligenes faecalis were isolated from the textile effluent samples collected from Nahar textile industry, Lalru (Punjab). Both these isolates have high decolourization potential and take only 24 h for complete decolourization. Different parameters, such as carbon source, nitrogen source, temperature, pH, concentration of dyes and inoculum size were optimized for decolourization of remazol black, direct blue and acid orange which are azo dyes that are most widely used and are highly toxic. Bacillus flexus showed 100% decolourization after 20 h with acid orange and at 24 h for remazol black and direct blue. Alcaligenes faecalis showed the best incubation time for all the three dyes to be 24 h and the extent of decolourization was found to be 89, 98 and 100% for remazol black, direct blue and acid, respectively. Such decolourizing potential of the isolates is quite high as compared to the earlier reports and can be effectively used as a tool for bioremediation of various textile effluents. Keywords: Acid orange, Aquatic pollution, Bioremediation, Direct blue, Dyes, Effluent treatment, Remazol black, RSM Worldwide, industrial waste products, untreated in particular, pollute the environment gravely. In many cases, such contaminations are problematic because of persistence and toxicity. Synthetic dyes produced in huge quantity (>7×10 5 tons annually) worldwide for use in textile dying, paper printing, colour photography, cosmetic industry and as additives in petroleum products are one such major concern. Among these dyes, azo dyes are the most widely used and account for >60% of total number of dye structures manufactured 1,2 . Waste water discharge from the textile industries is highly coloured and toxic. These dyes not only cause problems due to aesthetic reasons but are also detrimental to aquatic life. Some fraction of these pollutants percolates into the underground water rendering it unfit for drinking. It is estimated that about 10-15% of dyes are lost in the effluent during the dying process which is aggravating the pollution problem 3,4 . Viable biological processes have received increasing interest owing to their cost effectiveness, ability to produce less sludge, and environmental benignity 5 . Many studies on the decolourizing capability of micro- organisms have been reported, including bacteria 6-10 , fungi 11,12 , yeast 13 , actinomycetes 14 and algae 15 . In most of the studies, decolourization is occurring in many days with significantly low rate of decolourization or the microorganisms are capable of degrading at very low concentration of dyes. Bacillus sp. and Pseudomonas sp. have showed 89% of decolourization of Orange 3R at 144 h followed by 80 and 76% by Salmonella sp. and Klebsiella sp., respectively 16 . Pseudomonas aeuroginosa is reported to remove the colour of the remazol black B azo dye from 85 to 94.4% after 5 days 17 . High concentration of dyes has often been found toxic to bacterial strains and above 50 ppm inhibits bacterial growth and its enzymatic activities. For treatment of textile effluent, we need to isolate microorganisms that are capable of degrading the dyes completely, even at high concentration, as carried by the textile effluents. The present study mainly focuses on isolation of bacterial strains that have high decolourization potential for complete decolourization of all the three azo dyes that are detrimental for human health in lesser time, in economical and eco-friendly way. Materials and Methods Isolation and screening of azo dye degrading microorganisms Textile effluent was collected from Nahar textile industry, Lalru, Punjab. For isolation of microorganisms, ————— *Correspondence: E-mail: jksharmakuk@rediffmail.com, jsharma@kuk.ac.in