Bacterial Enzymes and Multi-enzymatic Systems for Cleaning-up Dyes from the Environment - Microbial Degradation of Synthetic Dyes in Wastewaters - page 28

and Kaushik 2009 ). The capacity of laccases to produce polymeric products also
makes them a useful tool for organic synthesis (Riva 2006 ; Madhavi and Lele 2009 )
and in addition, are also potential enzymes for biosensors or biofuel cells
(Wheeldon et al. 2008 ; Willner et al. 2009 ). Peroxidases are heme-containing
proteins that use hydrogen peroxide (H 2 O 2 ) or organic hydroperoxides (R-OOH) as
electron accepting co-substrates while oxidizing a variety of compounds. Due to
their catalytic versatility and enzymatic stability, peroxidases are of particular
interest for industrial redox conversion processes (Hofrichter et al. 2010 ). Among
peroxidases, a new super family has arisen, the so-called dye-decolorizing perox-
idases (DyPs) (Sugano 2009 ; Hofrichter et al. 2010 ; Colpa et al. 2013 ). These
enzymes are known to successfully oxidize a wide range of substrates, but most
importantly, they highly degrade high redox synthetic dyes, such as anthraquinone
and azo dyes. In this paper, we have reviewed the enzymatic properties, mecha-
nisms and toxicity of dye-degradation products of different bacterial enzymes and
also the properties of in vitro and in vivo multi-enzymatic systems for the decol-
orization of synthetic dyes.

2 Biotransformation of Dyes Using Laccases

Laccases are a part of the large multi-copper oxidase family of enzymes that cat-
alyze the four-electron reduction of oxygen to water (at the T2 T3 trinuclear Cu

centre) by the sequential one-electron uptake from a suitable reducing substrate (at
the T1 mononuclear copper centre) (Solomon et al. 1996 ; Stoj and Kosman 2005 ).
Most of the known laccases have fungal (e.g. white-rot fungi) or plant origins.
However, many laccases have been isolated from bacteria in the last decade (Claus
2003 ; Giardina et al. 2010 ). Fungal laccases are the enzymes used in the vast
majority of the studies in the literature, but bacterial laccases show advantages for
biotechnological processes due to the lack of post-translational modi

-

cations, their
higher yields of production, easiness of manipulation and improvement by protein
engineering approaches.

2.1 Decolorization Capacity of Bacterial CotA-Laccase

The rst study, using bacterial laccases for synthetic dyes decolorization, was

performed with recombinant CotA-laccase from Bacillus subtilis, which is a bac-
terial thermoactive and intrinsically thermostable enzyme (with half-life of 2 h at
80

°

C), showing the predictable robustness for biotechnological applications
(Pereira et al. 2009a , b ). Twenty two synthetic dyes, both anthraquinonic and
azo dyes, were found to be degraded to different extents, after 24 h of reaction by
CotA-laccase (Fig. 1 ).