Bacterial Enzymes and Multi-enzymatic Systems for Cleaning-up Dyes from the Environment - Microbial Degradation of Synthetic Dyes in Wastewaters - page 47

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AR266 AB194 DB38 RB5 RY145 DR80 SOG MB9 MB17 MB3

Azo dyes

Fig. 17 Inhibitory effects of intact dyes over Saccharomyces cerevisiae (black bars) and upon the
stepwise treatment with PpAzoR followed by CotA (white bars) (adapted fromMendes et al. 2011a )

4.4 Construction of an E. coli Strain Producing Both
Azoreductase and Laccase

The use of whole cell catalysis is considered one of the most appropriate systems
for biodegradative processes. It allows the lowering of the costs associated with
enzyme puri

cation and co-factors supply and also providing protection to the
biocatalysts from harsh process environment. Therefore, a host strain co-expressing
the genes coding for both enzymes of interest, PpAzoR and CotA, was constructed
and a whole cell system was tested for the decolorization of dyes (Mendes et al.
2011a ).
Three model dye-containing wastewaters were designed to mimic textile ef u-

ents produced during cotton or wool textile dyeing processes containing other
additives and salts (30

90 % of the total weight) in addition to dyes (Prigione et al.
2008 ; Mendes et al. 2011b ). These dyes are representative of different structural dye
types and are widely applied in the textile industry. A step-wise sequential process
was set-up, where the sequential action of PpAzoR and CotA enzymes could be
tuned by aeration conditions. Whole cells remained in anaerobic conditions for
24 h, appropriate for PpAzoR degradation of azo dyes to aromatic amines, followed
by a second 24 h period where with appropriate shaking, CotA aerobically oxidized
the aromatic amines, and also the anthraquinonic dyes present in the model dyes
(Mendes et al. 2011a ). This procedure resulted in almost 100 % decolorization
levels for the acid dye bath and around 80 % for both the reactive and direct dye
baths (Fig. 18 a). After this sequential treatment the toxicity levels of the

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nal
products was reduced for both S. cerevisiae model growth or for C. elegans
reproduction (Fig. 18 b).
Taken together, the results showed that the genetically engineered E. coli strain
expressing the gene coding for azoreductase and laccase is able to decolorize and
detoxify to a signi cant level the 3 model wastewaters tested, highlighting its