Montira Leelakriangsak and Sukallaya Borisut

pp. 509 - 516

Abstract

The product of the Bacillus subtilis gene azoR1 is annotated as a putative azoreductase, production of which is
induced in response to thiol-reactive compounds. Here we report on the decolorization of four azo dyes by azoreductase
activity. The ability of overexpressed AzoR1 strain ORB7106 to catalyze decolorization of azo dyes was investigated on agar
plates and in liquid cultures. The decolorization efficacy of a mutant, ORB7106, which has lost negative control of azoR1
expression, was significantly better than the parental strain (JH642), providing evidence that the azoR1 gene product is
an azoreductase with the ability to decolorize azo dyes. ORB7106 showed 40-98% azo dye decolorization within 48 h. The
bacterium exhibited a remarkable color removal capability over a wide range of Methyl Red concentrations (10-200 mg l^-1), pH
(5-9) and temperatures (25-45°C). A significant increase in the decolorization activity was observed after induction of AzoR1
production. The results suggested that AzoR1 production could be induced by Methyl Red. The decolorizing activity is
primarily associated with the cytosolic fraction and requires NADH as a cofactor.