The Biodegradation of Azo Dyes by Actinobacteria - Microbial Degradation of Synthetic Dyes in Wastewaters - page 300

Immobilized nano-particles and bacterial cells have shown promising results in the
dye degradation (Lachheb et al. 2002 ; Daneshvar et al. 2005 ).
From these studies, it may be concluded that oxidative enzymes, produced by
actinomycetes in the presence of some redox mediators, may have a practical
application in the degradation of azo dyes.

5 Factor Affecting Biodegradation of Azo Dyes

The effectiveness of any biological treatment depends on the environmental con-
ditions. The thermal stability and functioning of the enzyme in the Actinobacteria
strain is very important for practical application. The isolation of Streptomyces spp.
from unusual environment may produce a variety of bioactive compounds (Chro-
nakova et al. 2010 ; Gousterova et al. 2014 ).Therefore, it is urgent to isolate and
identify strains that can survive and maintain their activities under varying envi-
ronmental conditions.
Thermostable laccases have been isolated from various strains of actinomycetes
(Endo et al. 2003 ; Suzuki et al. 2003 ; Lu et al. 2013 ). Thermostable laccases have
been also reported in Actinobacteria, such as Streptomyces lavendulae REN-7,
Streptomyces griseus and Streptomyces sp. C1, which retained their original activity
even at 70

C (Endo et al. 2003 ; Suzuki et al. 2003 ; Lu et al. 2013 ). Recently,
Sahasrabudhe and Pathade ( 2013 ) reported degradation of reactive orange dye
using Georgenia sp. CC-NMPT-T3 at 28

°

C. The actinobacteria could decol-
orize 94.2 % reactive orange dye (50 mg l − 1 ) within 8 h. In general, most laccases
have an optimum enzymatic reaction at an acidic pH and the optimum temperature
about 30

45 °

-

C (Baldrian 2006 ). Lu et al. ( 2013 ) reported optimum activity of laccase
enzyme isolated from Streptomyces sp. C1 at pH 8.0. Moreover, this enzyme was
capable of retaining 70 and 50 % of its initial activity after 3 h incubation at pH
11.0 and 12.0, respectively. This demonstrated that the enzyme showed a moderate
resistance to alkaline conditions. Mane et al. ( 2008 ) reported pH 8.0 as the best
suitable condition for Streptomyces krainskii strain SUK-5 for optimal decolor-
ization of reactive blue-59 dye. Similarly, Georgenia sp. CC-NMPT-T3 was able to
degrade the azo dye reactive orange at pH 6

°

8 in static anoxic conditions (Saha-

-

srabudhe and Pathade 2013 ).
Previously, azo reductase activities have been reported in static conditions in
several species of Actinobacteria, such as Streptomyces coelicolor, Nocardia cor-
allina and Nocardia globerula (Yatome et al. 1991 ; Bhaskara et al. 2003 ; Chou
et al. 2005 ; Chengalroyen 2011 ). However, agitation (aerobic) is more effective in
case of laccase enzyme and lignin-degrading enzymes. Actinobacteria Georgenia
sp. CC-NMPT-T3, Streptomyces cyaneus CECT 3335, Streptomyces krainskii
SUK-5 and Streptomyces sp. C1 have been reported to perform their activities best
under aerobic conditions (Mane et al. 2008 ; Lu et al. 2013 ; Sahasrabudhe and
Pathade 2013 ).