Bacterial Enzymes and Their Role in Decolorization of Azo Dyes - Microbial Degradation of Synthetic Dyes in Wastewaters - page 154

6.1.6 Veratrol Alcohol Oxidase (VAO)

The enzyme veratrol-alcohol oxidase was catalyzes the chemical reaction as:

Aromatic primary alcohol þ O 2 Aromatic aldehyde þ H 2 O 2

Hence, this enzyme has two substrates i.e. aromatic primary alcohol and O 2 and
their products are aromatic aldehyde and H 2 O 2 . This enzyme belongs to the family
of oxidoreductases. VAO catalyzed the oxidation of aryl

α - and α - ʲ - unsaturated

ʳ -alcohols to the corresponding aldehydes with concomitant reduction of O 2 to

H 2 O 2 . The formation of H 2 O 2 can be determined by the method as suggested by
Tamboli et al. ( 2011 ).

6.2 Mediated Biological Azo Dye Reduction

The high molecular weight sulfonated azo dyes are unable to pass through the cell
membrane (Levine 1991 ). It was suggested that the reduction of these dyes could
occur through the mechanism that are not dependent on transport into the cell
membrane. Many reports were available on the role of redox mediators in azo bond
reduction by bacteria under anaerobic conditions (Keck et al. 1997 ; van der Zee
et al. 2001a ; Dos Santos et al. 2004 ). Ribo

cantly enhanced the
reduction of mordant yellow 10 by anaerobic granular sludge (Field and Brady
2003 ). 1-amino 2-napthol, one of the constituent amines of the azo dye, AO7,
increased its decolorization rate, possibly by mediating the transfer of reducing
equivalents (Mendez-Paz et al. 2005 ). The addition of synthetic electron carriers,
such as anthraquinone-2,6-disulphonate, could also greatly enhance the decolor-
ization of many azo dyes (van der Zee et al. 2001b ). Keck et al. ( 1997 ) were

avin signi

rst
example of the anaerobic cleavage of azo dyes by redox mediators formed during
the aerobic degradation of a xenobiotics compound. Cell suspensions of Sphingo-
monas sp. strain BN6, grown aerobically in the presence of 2-naphthyl sulfonate
(NS), shown 10

20 fold increase in decolorization rate of an azo dye under
anaerobic conditions. Even the addition of culture

-

ltrates from these cells could
enhance anaerobic decolorization by cell suspensions grown in the absence of NS.
Redox intermediates generated during the aerobic degradation of aromatic com-
pounds were act as enhancer in dye decolorization reactions under anaerobic
condition (Keck et al. 1997 ; Chang et al. 2004 ).