Bacterial Enzymes and Their Role in Decolorization of Azo Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 146

reductase (Dos Santos et al. 2007 ; Pandey et al. 2007 ). However, this chapter has
focused on the various oxidoreductive enzymes involved in decolorization and
detoxi

cation of textile azo dyes and their mechanism of azo dye decolorization.

2 Bacterial Decolorization of Textile Azo Dyes

Bacteria degrade the textile dyes under both aerobic and anaerobic conditions. The
optimum pH for decolorization of textile dyes varied from acidic to basic range.
The bacteria, used for decolorization of textile dyes, were isolated from textile dye
contaminated soil by enrichment techniques and identi ed on the basis of 16s

rRNA sequence and biochemical characteristics (Kalyani et al. 2008 ; Dawkar et al.
2008 ; Dhanve et al. 2008a , b ; Telke et al. 2008 ). However, certain microorganism,
which was not isolated from textile dye-contaminated soil, but showed excellent
dye decolorization property.

3 Decolorization of Azo Dye Under Anaerobic Condition

At present, only mechanism of azo dye decolorization under anaerobic condition is
well known. Anaerobic azo dye reduction involves the reduction of azo bond by the
transfer of reducing equivalents resulting in the formation of aromatic amines
(Chung and Cerniglia 1992 ). As removal of a large amount of azo dyes from
wastewater is a major concern, research on bacterial azo dye reduction has mainly
focused on the activity of (facultative) anaerobic bacteria. Various anaerobic bac-
teria were used in bioreactor for treatment of textile ef uent containing azo dyes

(I şı k and Sponza 2005 ; Maas and Chaudhari 2005 ; Mezohegyi et al. 2008 ).

4 Decolorization of Azo Dyes under Anoxic Condition

Pure bacterial strains, such as Pseudomonas luteola, Aeromonas hydrophila,
Bacillus subtilis, Pseudomonas sp. and Proteus mirabilis were utilized for azo dyes
decolorization under anoxic condition (Chen et al. 1999 , 2003 ; Chang et al. 2001 ;
Yu et al. 2001 ). Although, most of these cultures were able to grow aerobically, but
decolorization were achieved only under anaerobic conditions. Anoxic decoloriza-
tion of various azo dyes by mixed aerobic and facultative anaerobic microbial
consortia has been reported by many researchers (Nigam et al. 1996 ; Kapdan et al.
2000 ; Padmavathy et al. 2003 ; Khehra et al. 2005 ; Moosvi et al. 2005 ). Azo dye
decolorization by pure as well as mixed cultures have required complex organic
carbon sources, such as, yeast extract, peptone, or a combination of complex organic
source and carbohydrate (Chen et al. 2003 ; Khehra et al. 2005 ). The decolorization