The azo dye, Reactive Black B (RBB), was decolorized by a wild-type isolate (Pseudomonas luteola), an Escherichia coli mutant (E coli NO3), and a recombinant strain (E coli CY1) harboring decolorizing genes from Rhodococcus sp. Decolorization of RBB by P luteola was inefficient with only 65% conversion, while color removal exceeded 90% for the two E coli strains, which were further investigated to determine the decolorization kinetics and operational stability. Kinetic studies applying a Monod-type model showed that E coli NO3 was a more effective decolorizer for RBB than the CY1 strain. In addition, decolorization of RBB with the NO3 strain could tolerate higher temperatures and was more kinetically favorable over CY1. The optimal pH for decolorization was around 6.0-8.0 for NO3 and 8.0-10.0 for CY1. Decolorization of RBB was inhibited when the dissolved oxygen level exceeded 0.35 mg dm(-3) for both strains. E coli NO3 was more stable during repeated operations, whereas the decolorization activity of E coli CY1 slightly decreased when the strain was used repeatedly. (C) 2004 Society of Chemical Industry.