Bacterial Degradation of Azo Dye Containing Wastes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 59

also help in exploring the mechanisms of biodegradation using the tools of
biochemistry and molecular biology. This information could be also useful in
modifying the strains with enhanced enzyme activities for faster degradation of dyes
(Saratale et al. 2011 ).

2.2 Bacterial Degradation of Azo Dyes by Mixed Cultures
and Consortia

Due to the chemical complexity of dye containing wastewater, it is necessary to
develop more ef

cient microbial processes for decolorization. Pure strains are often

speci c to a type of dye and have a narrow range for different azo dyes decolor-

ization. However, at eld level, it is not possible to have mono culture process due

to a large volume of wastewater containing different dyes. Hence, mixed cultures
are particularly more useful in such situation, as microbial consortia can collectively
carry out biodegradation which is not possible with individual pure strain. A sig-
ni

cant advantage of consortia or mixed culture over the use of individual strains is
that different strains can attack the dye molecule at different positions or may utilize
toxic metabolites produced by the co-existing strains for further decomposition. No
doubt treatment systems having mixed microbial populations achieve a higher
degree of biodegradation and mineralization due to their synergistic metabolic
activities (Nigam et al. 1996 ). The complete degradation of chemical substances is
only possible in the presence of several enzymes produced by the mixed cultures
(Khehra et al. 2005 ).
In general, initial cleavage of the azo bonds takes place, during azo dye deg-
radation which results into the production of aromatic amines, which are often toxic
in nature. However, in the presence of microbial consortium, these aromatic amines
get degraded by complementary organisms, making the process more effective and
ef

cult to isolate a single
bacterial strain from dye-containing wastewater samples and long-term adaptation
procedures are needed for effective decolorization and degradation of azo dyes. On
the other hand, mixed cultures only provide an average macroscopic view of what is
happening in the system. In this case, the results are not easily reproduced and
interpretation of the results is also quite dif

cient (Moosvi et al. 2005 ). No doubt it is very dif

cult. Moosvi et al. ( 2007 ) reported three
isolates Micrococcus sp., M. luteus, and P. polymyxa, when used in mixed culture
were able to decolorize nine dyes but when individually used, they were found to be
inef cient for dye removal. Similar results were also reported by Nigam et al.

( 1996 ). They also did not observe decolorization by a single strain but with a
consortium, a wide range of dyes were effectively reduced. A consortium, con-
sisting of four bacterial isolates, P. putida, B. cereus, P.

uorescence and Steno-
trophomonas acidaminiphila, decolorized C.I. acid red 88. The dynamics of
consortia capable of faster methyl red biotransformation was monitored which
revealed Klebsiella sp., Buttiauxella sp. and Bacillus sp. as the main population