The Biodegradation of Azo Dyes by Actinobacteria - Microbial Degradation of Synthetic Dyes in Wastewaters - page 292

Onat et al. 2010 ). However, physico-chemical methods generally produce a huge
amount of additional residues that make these methods non eco-friendly (Sharma
et al. 2013 ). Complete mineralization of dyes with microorganisms is one of the
most viable options for remediation of industrial ef

uents containing azo dyes. The
versatility of microorganisms and their various metabolic pathways can be used to
target the major chemical classes of dyes (Mohanty et al. 2006 ; Sadettin and
Donmez 2007 ; Liu et al. 2011 ; Saratale et al. 2011 ; Khalid et al. 2012 ; Prasad and
Aikat 2014 ). Although a variety of culturable bacteria, fungi and algae, capable of
degrading dyes through the oxidoreductase enzymes, have been intensively studied
(Table 1 ), but a group of microorganisms, such as actinomycetes, has not previ-
ously been focused much for their biodegradability potential.
Actinomycetes belong to Enterobacteriaceae family and now, they are known for
their degradation capabilities. Actinobacteria are considered a very attractive option
for the production of many secondary bioactive compounds which are metabolites
(Nathan et al. 2004 ; Jensen et al. 2005 ; Suthindhiran and Kannabiran 2009 ).
Actinobacteria are a group of lamentous Gram positive bacteria which are known

as prokaryotes with high GC contents (Stackebrandt et al. 1997 ; Deepika and
Kannabiran 2009 ; Deepika et al. 2009 ). They are widely distributed in terrestrial
and aquatic ecosystems (Chronakova et al. 2009 ), Streptomyces spp. in soil consist
of 50 % of the total microbial population and play a crucial role in the recycling of
refractory biomaterials by decomposing complex mixtures of polymeric materials
from dead plants, animals and fungi. Considering their diverse habitat and role in
the environment, these microorganisms can be studied for their potential for bio-
degradation and bioremediation of contaminated soil and aquatic environment.
Very recently, Streptomyces species have been exploited for the degradation of
synthetic dyes (Lu et al. 2013 ; Gousterova et al. 2014 ). Researchers have developed
a great interest in actinomycetes because of their high potential in the treatment of
industrial waste (Gousterova et al. 2011 ). Actinobacteria are particularly suitable for
the wastewater treatment, because of their different metabolic pathways working in
a wide range of environmental conditions and survival under extreme conditions.
Microorganisms, isolated from extreme environments, were found to be producers
of enzymes and metabolites with promising properties (Lee et al. 2012 ; Mahajan
and Balachandran 2012 ). In this chapter, the role of actinomycetes in the degra-
dation of azo dyes is discussed thoroughly.

2 Environmental Concerns of Azo Dyes

Azo dyes and their intermediates are toxic, mutagenic and carcinogenic (Lu et al.
2010 ; Modi et al. 2010 ) and affect organisms in both aquatic and terrestrial systems
(Puvaneswari et al. 2006 ). Among azo dyes, those produced from aromatic amines,
such as benzidine and 4-biphenylamine, 4-aminobiphenyl, monoacetylbenzidine
and acetylaminobiphenyl, pose a serious threat to the environment and human
health (Manning et al. 1985 ; Cerniglia et al. 1986 ; Choudhary 1996 ; Chung 2000 ).