Microbe-Mediated Degradation of Synthetic Dyes in Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 222

Fig. 8 Mechanism of
reactive orange 16
degradation by the white rot
fungus I. lacteus, the
compound in bracket was not
detected (Svobodova et al.
2007 )

LC-MS analyses. The proposed degradation pathway has been elucidated in Fig. 8 .
However, other fungal Lac enzymes can cause polymerization. Different enzymes
can be induced in a certain microorganism depending on the structure of the azo
dyes (Fig. 9 ). In the presence of GYHER, an induction of Lac was observed in
Galactomyces geotricum (Waghmode et al. 2011 ); whereas in the presence of
Remazol Red, an induction of azoreductase and Lac was demonstrated. However,
the proposed mechanisms for these dyes do differ. The degradation of GYHER
starts with the asymmetric cleavage of the azo bond, which is catalysed by Lac,
whereas the degradation of Remazol Red begins with the symmetric cleavage of the
azo linkage, which is catalyzed by an azoreductase, followed by an asymmetric
oxidative cleavage (Waghmode et al. 2011 , 2012 ). The degradation of Remazol
Red, Rubine and GYHER by Brevibacillus laterosporus is also dependent on the
structure of the dye (Fig. 10 ). A signi

cant increase was observed in the activity of
azoreductase, NADH-DCIP reductase, veratryl alcohol oxidase and tyrosinase in
cells obtained after the decoloration of Remazol Red and GYHER. However, the
suggested degradation mechanisms for these two colorants are different. Further-
more, while NADH-DCIP reductase and ribo

avin reductase were induced, a
complete inhibition of azoreductase was observed during the decoloration of
Rubine (Kurade et al. 2011 ; Waghmode et al. 2011 ). The use of microorganisms,
that excrete various oxidases and reductases, can completely degrade azo dyes and
detoxify contaminated water from the textile industry.