Bacterial Enzymes and Multi-enzymatic Systems for Cleaning-up Dyes from the Environment - Microbial Degradation of Synthetic Dyes in Wastewaters - page 48

( a) (b)

120 120

100 100

80

80

60 60

40

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20

20

0

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Acid Reactive Direct Acid Reactive Direct

Model Wastewater Model Wastewater

Fig. 18 a Residual color after the stepwise sequential process using whole cells co-producing
PpAzoR and CotA (white bars). b Toxicity over Caenorhabditis elegans reproduction of intact
model wastewater (black bars) and after the stepwise sequential process using whole cells co-
producing PpAzoR and CotA (white bars) (Mendes et al. 2011a )

potential as a degradative and detoxifying bio-system for the treatment of real dye-
containing ef uents, without the costs associated with enzyme puri cation and

cofactors addition.

5 Conclusions and Future Perspectives

Synthetic dyes impart an intense color to wastewater ef uents from the textile,

leather or other dye manipulating industries leading to environmental, medical and
aesthetic problems. The diversity and complexity of dyes present in these ef

uents
are designed to resist fading on exposure to light or chemical attack, pose serious
problems on the design of technically feasible and cost-effective treatment meth-
ods. There are a relatively low number of known enzymes that are ef ciently

involved in the degradation of synthetic dyes in natural systems. Therefore, the
characterization of enzymes, that make a discernible contribution to the degradation
of synthetic dyes, paves the way for the improvement of multi-enzymatic systems,
through protein engineering strategies, to maximize their biodegradation, bio-
transformation and valorization potential. In this review, we have described the
properties, enzymatic mechanisms and products toxicity of three different types of
bacterial enzymatic systems. The CotA-laccase from B. subtilis is a promising
enzyme for the oxidative degradation of both antraquinonic and azo dyes in
addition to their ef ciency in the biotransformation of toxic aromatic amines (the

degradation products of azoreductases). The azoreductase PpAzoR from P. putida
MET94 is an enzyme that uses a broad range of azo dyes as substrates leading to
high levels of decolorization. The major drawback associated with the use of