Bacterial Enzymes and Their Role in Decolorization of Azo Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 149

Fig. 1 Reaction catalyzed by
azo reductases. a Methyl red;
b 2-Amino benzoic acid;
c p-dimethyl amino anilline

COOH

N(CH 3 ) 2

NN

(a)

2 NADH + H + or NADPH + H + or
FADH 2

2 NAD + or NADP + or
FAD +

COOH

H 2 N N(CH 3 ) 2

NH 2

(c)

(b)

there are a few reports on systems which are involved in the transport into bacterial
cells of other sulfonated substrates, such as p-toluene sulfonate, taurine and alkane
sulfonates (Locher et al. 1993 ; Eichhorn et al. 2000 ). The 2-ABS degrading
Alcaligenes sp. strain O-1 can utilize two other aromatic sulfonates, benzene and
toluene sulfonate, for growth. However, cell extracts of this strain can desulfonate
at least six substrates (Thurnheer et al. 1986 ). This suggests that the presence of
highly speci c transport systems for the uptake of aromatic sulfonates in these

cultures. Azo reductase and avin reductase are the potent enzymes involved in the

decolorization of azo dyes, but generate the toxic amines after reduction of azo
bond. The reaction catalyzed by azo reductase has been shown in (Fig. 1 ).

6.1.2 NADH-DCIP Reductase and Malachite Green Reductase

Signi c reductase, such as NADH-DCIP reductase and

Malachite green reductase during decolorization of azo dyes suggests their possible
participation in decolorization (Kalyani et al. 2008 ; Telke et al. 2008 ). The function
of non-speci

cant induction of non-speci

c reductases is still unknown. NADH-DCIP reductase belongs to the
bacterial mixed function oxidase system may takes part in the detoxi cation of

xenobiotic compounds (Salokhe and Govindwar 1999 ). NADH-DCIP reductase
enzyme reduced DCIP substrate using NADH as electron donor. DCIP is a blue in
its oxidized form and it becomes colorless after reduction. The signi

cant induction

of non-speci c reductase in the biodegradation of Malachite green was observed

and termed as MG reductase (Parshetti et al. 2006 ). MG-reductase enzyme reduced
Malachite green into leucomalachite green using NADH as electron donor. The
reactions catalyzed by DCIP-reductase and MG- reductase have been re ected in

Figs. 2 and 3 .