The Biodegradation of Azo Dyes by Actinobacteria - Microbial Degradation of Synthetic Dyes in Wastewaters - page 299

lignin peroxidases and veratryl alcohol was found to enhance the decolorization of
azo and anthraquinone dyes (Joshi et al. 2010 ). The role of lignin-degrading
enzymes in the treatment of contaminated ef

uent is very critical, as it demands a
thorough understanding of lignin degrading organisms and their enzyme systems.
The laccases produced by Streptomyces were also found to be very effective for the
decolorization of textile dyes (Dube et al. 2008a ; Molina-Guijarro et al. 2009 ;Lu
et al. 2013 ). Gottlieb et al. ( 2003 ) demonstrated the usefulness of a laccase enzyme
produced by Streptomyces cyaneus CECT 3335 for the decolorization of azo dyes.
Often laccases are coupled to the reduction of oxygen to water along with
oxidation of various substrates (Kurniawati and Nicell 2007 , 2009 ; Morozova et al.
2007 ).The role of redox mediators is very important in a system for oxidative
degradation, since it mediates the movement of electrons in the system and
increases the degradation rate indirectly (Gonzalez-Gutierrez and Escamilla-Silva
2009 ). Lu et al. ( 2013 ) demonstrated the degradation of indigo carmine and dia-
mond black PV with syringaldehyde as mediator. In this study, eight strains with
laccase activity were isolated from composting samples in different phases, among
which a novel strain was identi ed laccase-

like multi copper oxidases (LMCO) of strain C1 showed a single protein band on
SDS-PAGE gel with a molecular mass of about 38 kDa. The novel laccase showed
alkaline resistance and moderate thermostability. The enzyme activity was activated
by some metal ions, such as Cu 2+ ,Co 2+ and Fe 3+ at the concentration of 1 mM,
while it was strongly inhibited in the presence of Hg 2+ .
Some studies showed that two-domain small laccase isolated from Streptomyces
species could tolerate high temperature and alkaline conditions (Steger et al. 2007 ;
Dube et al. 2008a ; Molina-Guijarro et al. 2009 ) and also caused degradation of
pigment and phenolic compounds along with antibiotic formation (Nakamura et al.
2003 ; Molina-Guijarro et al. 2009 ). The ability of a laccase (EC 1.10.3.2), produced
by Streptomyces cyaneus CECT 3335, to decolorize and detoxify azo dyes was also
assessed by Moya et al. ( 2010 ). Acetosyringone was used as the redox mediator in
this study. A signi

ed as Streptomyces sp. C1. The puri

cant decrease in the toxicity of the dyes, New Coccine and
Chromotrope 2R, was observed after the decolorization process. Laccases had a
large catalytic versatility due to their low substrate speci

city against phenolic
compounds and aromatic amines. In the presence of redox mediators, these
enzymes can extend their oxidative action even to non-phenolic compounds
(Bourbonnais and Paice 1990 ; Call and M cke 1997 ). A large number of phenolic

compounds were produced by the selected Streptomyces strains, when grown under
solid state fermentation conditions on wheat straw (Hernandez-Coronado et al.
1998 ). These compounds can act as natural mediators. Usually these compounds
are produced by microorganisms during their growth or lignin depolymerisation
(Camarero et al. 2005 ), whereas Maneet al. ( 2008 ) isolated lignin peroxidase from
Streptomyces krainskii SUK-5. In the presence of this enzyme, reactive blue-59 dye
was completely degraded in less than 24 h. Recently, titanium oxide nano-particles
(TiO2 NPs) were synthesized from the marine Actinobacteria (Priyaragini et al.
2013 ). Actinobacteria crude extract and NP synthesized TiO2 were found very
effective for the degradation of azo dyes, such as acid red 79 and acid red 80.

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