Microbe-Mediated Degradation of Synthetic Dyes in Wastewater - Microbial Degradation of Synthetic Dyes in Wastewaters - page 221

3 Factors Controlling Microbial Decolorization Process

Microorganisms are sensitive to the presence of chemical substances, such as dyes,
high salinity, variations in pH and high content of organic compounds (Dua et al.
2002 ; Ang et al. 2005 ; Megharaj et al. 2011 ). For bioremediation processes, the
most useful microorganisms are those isolated from textile industry-contaminated
environments, uents and sludge from wastewater treatment

plants, as they are adapted to grow in the extreme conditions (Yang et al. 2009 ; Ola
et al. 2010 ; Ayed et al. 2011 ). The biodecoloration process is dependent on the
following factors: the azo dye structure, carbon and nitrogen sources, salinity, pH,
temperature, dye concentration and the presence or absence of oxygen.

including soil, ef

3.1 Effects of the Azo Dye Structure

It has been observed that the enzymatic degradation of the dye is highly in uenced

by its structure (Pasti-Grigsby et al. 1992 ; Hsueh et al. 2009 ; Kuberan et al. 2011 ;
Rajee and Patterson 2011 ). For example, azo dyes with electron-withdrawing
groups, such as SO 3 − , are easier to degrade than those with electron-releasing
groups, such as

NH-triazine. Therefore, azo dyes, that contain more electron
withdrawing groups, show faster decoloration, and if these groups are in the para or
ortho positions to the azo bond, the degradation proceeds faster than if they are in
the meta position, because they provide a more effective resonance effect, causing
azo dyes to be highly electrophilic and resulting in faster reductive decoloration
(Pricelius et al. 2007 ; Tauber et al. 2008 ; Hseuh et al. 2009). Recent studies have
revealed that the enzymatic activity is induced by the presence of dyes in such a
way that this activity is signi

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cantly higher at the end of the decoloration process.
For example, Reactive Black 5 induces MnP activity in Debaryomyces polymor-
phus (Yang et al. 2005 ) and Trichosporon akiyoshidainum and Lac activity in
Trametes versicolor (Fernandez et al. 2009 ); azoreductase activity is improved in
Chlorella vulgaris by the addition of G-Red, in Nostoc linckia by Methyl Red (El-
Sheekh et al. 2009 ) and in Scenedesmus bijugatus by Tartrazine and Ponceau
(Omar 2008 ); Reactive Blue 221 induces Tyr in T. akiyoshidainum (Pajot et al.
2011 ); Lac activity is enhanced in Pleurotus sajorcaju in the presence of Acid Blue
80, Acid Green 28 and Reactive Red 198 (Munari et al. 2008 ) and in Galactomyces
geotrichum by a mixture of Remazol Red, Golden Yellow HER, Rubine GFL,
Scarlet RR, Methyl Red, Brown 3 REL and Brilliant Blue (Waghmode et al. 2011 ).
In the process of azo dye biotransformation, different types of enzymes, both
oxidases and reductases, can be involved. During the decoloration of Reactive
Orange 16 by Irpex lacteus, signi cant activity of Lac and MnP was found with the

formation of three metabolites, but no polymerization products were detected by