Textile Dyes Degradation: A Microbial Approach for Biodegradation of Pollutants - Microbial Degradation of Synthetic Dyes in Wastewaters - page 191

Decolorization of dye is related to the presence of extracellular peroxidases,
particularly manganese peroxidases (Gold et al. 1988 ). However, an evidence,
relating degradation of polymeric dyes to phenol-oxidizing enzymes and to lignin
degradation, is largely circumstantial. Paszczynski and Crawford ( 1991 ) reported
involvement of veratryl alcohol during the degradation of some azo compounds by
P. Chrysosporium ligninase. Veratryl alcohol stimulated azo dye oxidation by
ligninase, acting as a third substrate (with H 2 O 2 and the azo dye) to cycle the
enzyme back to its native state. These studies report aerobic biodegradation of some
of the commercial textile dyes by P. Chrysosporium. The fungal lignin-degrading
system was implicated in the decolorization process, since crude lignin peroxidase
was required for the initial step of decolorization of Orange II and Tropaeolin.
Paszczynski and Crowford ( 1991 ) showed that while ligninase recognized Acid
yellow 9 as a substrate, Mn(II) peroxidase was responsible for decolorization of
other azo dyes. The extracellular ligninolytic enzyme systems of these fungi have
been directly linked to the degradation of these compounds.
The other major group of extracellular oxidative enzymes, involved in the white-
rot fungal lignin degradative process, is laccases. The laccases of T. Versicolour
catalyze the initial oxidation step in the biotransformation of anthracene and benzo
[a]pyrene. This process involves either a direct laccase oxidation mechanism or an
indirect mechanism involving the participation of an oxidation mediator, such as
putative present in the ultraltrate fraction. In some experiments with P. Chrysos-
porium, manganese peroxidases were found to play a major role in the initial
breakdown and decolorization of high-molecular-weight chlorolignin in bleach
plant ef uents and also to transform other naturally occurring polymers, such as

lignite and sub-bituminous coals. This fungus demonstrated a better ability than the
actinomycetes to mineralize the azo dyes (Paszczynski et al. 1992 ).
The use of ligninolytic enzymes was investigated, but their production yields
were too low for industrial applications (Bajpai 1999 ). Commercial enzymes, such
as xylanases, are produced in the large quantities in Trichoderma reesei and hence
used for pulp bleaching (Bajpai 1999 ). Application of xylanases was shown to
decrease chlorine consumption, which is a environmental-friendly process on one
hand and also increases the

nal brightness of the pulp. Other enzymes, such as
laccases, have been studied for their in vivo capacity to degrade lignin (Mayer and
Staples 2002 ). Laccases are commercially available and produced in fungal strains,
such as Aspergillus sp. (Yever et al. 1991 ; Berka et al. 1997 ; Record et al. 2003 ).
Aspergillus niger was used to produce the feruloyl esterase for pulp bleaching
application (Record et al. 2003 ). A basidiomycetous fungus Ganodermaa lucidum
has been found as a suitable organism for removal of Rhodamine-B and Sandolan
rhodine. The decolorization of dyes, containing toxic chlorinated phenols used in
Kraft bleach dyeing, has been observed by several workers. Bennett et al. ( 1971 )
reported that brownish color of the ef

uent in the textile industry was due to
presence of chlorolignin. The ability of microfungi to degrade this component of
the ef uent has been studied by Cammarota and Santa-Anna ( 1992 ).

Adsorption of dyes to the microbial cell surface is the primary mechanism of
decolorization (Knapp et al. 1995 ). Wong and Yu ( 1999 ) reported adsorption of