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the mass transfer resistance between a dye and cells. For example, decolorization of
Victoria blue R by A. calcoaceticus increased with increasing the dye concentration
up to 450 mg 1
−
1
(Chen et al.
2011
). Likewise, Victoria blue decolorization by P.
chrysosporium ATCC 34541 was proved to be nearly independent of the dye
concentration over the range from 50 to 350 mg 1
−
1
(Gomaa et al.
2008
).
4 Role of Oxidoreductive Enzymes in the Degradation
Process
Detoxi
cation of synthetic dyes by various bacteria and fungi is often mediated by
oxidoreductases. The main oxidoreductive enzymes playing a role in TPM dyes
elimination are lignin peroxidases (LiP), E.C. 1.11.1.14, manganese peroxidases
(MnP), EC 1.11.1.13 and laccases (Lac), EC 1.10.3.2 (Kandelbauer and Guebitz
2004
).
Laccases are copper-containing enzymes which catalyze oxidation of phenolic
compounds with a simultaneous reduction of one dioxygen molecule to two mol-
ecules of water. Laccases can act in the presence of redox mediators, such as 2,2
′
-
azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), N-hydroxybenzotria-
zole (HBT) and 3-hydroxyanthranilic acid, which help them in breaking down
several dif
cult to degrade compounds including synthetic dyes (Kunamneni et al.
2007
). Based on the experimental evidence, a laccase-mediated dye decolorization
mechanism was proposed in Fig.
1
. MnP and LiP were also shown to take part in
the degradation of various polycyclic aromatic and phenolic compounds, including
synthetic dyes (Champagne and Ramsay
2005
; Yang et al.
2011a
,
b
,
2013
). Gen-
erally, peroxidases are hemoproteins that catalyze reactions in the presence of
hydrogen peroxide. MnP catalyzes transformation of phenolic compounds, which is
associated with Mn (II) to Mn (III) oxidation (Shin et al.
2005
). Similarly, LiP
Fig. 1 Mechanisms of dyes
decolorization catalyzed by
laccase (a) without and
(b) with the mediator
engagement
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