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Abstract
Azo dyes are aromatic compounds bearing one or more azo bonds with great structural variety that are
widely used in textile, foods, printing, tattooing, and cosmetics industries. They are frequently found in a
chemically unchanged form even after waste-water treatment, so they are regarded as pollutants. Recent studies
uncovered the control of
azoR1
gene expression in Gram-positive bacterium
Bacillus subtilis
. The
azoR1
gene
encodes a putative FMN-dependent NADH-azoreductase referred to as AzoR1. Azoreductases have been
characterized as enzymes that can decolorize azo dyes by reducing azo groups. The levels of
azoR1
transcription
and AzoR1 protein synthesis in
yodB
mutant cells (
B. subtilis
ORB7106) were increased confirmed by microarray
and proteomic analyses. This study demonstrated the ability of
B. subtilis
ORB7106 in decolorization of azo dyes
over the wide range of dye concentrations (10-200 mg/L), pH (5-9) and temperatures (25-45
q
C) on both agar
plates and liquid cultures. Appearance of clear zones around bacterial colonies due to the reduction of Methyl red
and Congo red were observed on agar plates at 25-45
q
C and pH 5-9. In liquid culture, high decolorization
efficiency (60-90%) was achieved within 24 hr of incubation for Methyl red and Congo red but decolorizing
activities were limited for Azobenzene and Orange G. These data indicate that the
azoR1
gene product is an
azoreductase displaying the ability to decolorize the azo dyes.
Keyword:
Decolorization, Azo dye, Azoreductase,
Bacillus subtilis
