The dye-decolourizing bacterium was isolated from a coconut coir sample and identified as a Kerstersia sp. by 16S rRNA sequencing. It decolourized aerobically seven different naphthalene-containing sulfortated azo dyes such as Amaranth, Fast Red E, Ponceau S, Congo Red, Orange II, Acid Red 151 and Acid Orange 12. The bacterium decolourized Amaranth, Fast Red E, Congo Red and Ponceau S by 100% (100 mg L-1) and the remaining three dyes Orange II, Acid Orange 12 and Acid Red 151 were decolourized by 84%, 73% and 44%, respectively in 24 h. About 1 g L-1 concentration of Amaranth and Ponceau S were decolourized within 24 h, whereas only 0.6 g L-1 of Fast Red E was decolourized in 24 It. On the other hand a mixture of all the three dyes at 1 g L-1 concentration was decolourized within 26 h. The oxygen insensitive azoreductase activity of cell extract with respect to Amaranth, Fast Red E and Ponceau S were 0.069, 0.061 and 0.038 units mg(-1) of protein respectively. The decolourization kinetics of the dyes with azoreductase enzyme supports the ping-pong mechanism. Further, the bacterium capable of decolourizing these naphthalene-containing sulfonated azo dyes required 0.5% of peptone, yeast extract and temperature of 38 degrees C for growth. (c) 2006 Elsevier Inc. All rights reserved.