Cleaning-up dyes in the environment
Enzymatic dye degradation
Oeiras, 02.10.09
Long-lasting colours in our clothes means degrading these dyes is a difficult task. Identifying enzymes that are able to effectively convert dyes into non-toxic products introduces an attractive alternative for textile effluent clean-up. Two recent papers by the Laboratory of Microbial and Enzyme Technology at ITQB and co-workers show how a recombinant enzyme is able to transform commercial azo and anthraquinone dyes to environmentally safer compounds.
CotA-laccase is an oxidoreductase present in spore coat of the bacterium Bacillus subtilis and its ability to decolourise a variety of synthetic dyes led the researchers to a thorough analysis of the enzymatic oxidative degradation of azo and anthraquinonic simple models, namely Sudan Orange G (SOG) and Acid Blue 62 (AB62).
The enzymatic processes were examined by a multidisciplinar approach that combined enzymology, electrochemistry, mass spectrometry (MS), nuclear magnetic resonance (NMR) and microbiology. The researchers identified the reaction intermediates and the main final products, and further proposed mechanistic pathways for the oxidation of both type of dyes by laccases.
Azo dyes account for about 50% of all dyes in the textile, food, pharmaceutical, leather, cosmetics, and paper industries and are, along with anthraquinonic dyes, the most common synthetic colorants released into the environment. Since most of the synthetic dyes are xenobiotic compounds, researchers also analysed the potential toxicity of SOG, AB62, and its degradation products, using a yeast-based bioassay. After two hours of treatment with CotA-laccase, the inhibitory effect of both dyes on yeast growth was significantly reduced highlighting the potential for the application of this bioremediation friendly system.
One million tons of synthetic dyes are produced every year. One tenth of this amount is released to the environment in wastewaters becoming an important environmental concern. Traditional physicochemical processes for dye removal are expensive, can generate large volumes of sludge, and usually require the addition of environmental hazardous chemical additives. Resorting to enzyme biotechnology could provide a better solution. Additionally, getting mechanistic insight into the enzymatic dye biotransformation process opens the door for the biosynthesis of novel dye compounds with low toxicological properties.
Original articles
Journal of Biotechnology 2009, 139(1): 68-77
Enzymatic biotransformation of the azo dye Sudan Orange G with bacterial CotA-laccase
Luciana Pereira, Ana V. Coelho, Cristina A. Viegas, Margarida M. Correia dos Santos, Maria Paula Robalo and Lígia O. Martins
Advanced Synthesis & Catalysis (2009), 351 (11-12): 1857 - 1865
On the Mechanism of Biotransformation of the Anthraquinonic Dye Acid Blue 62 by Laccases
Luciana Pereira, Ana V. Coelho, Cristina A. Viegas, Christelle Ganachaud, Gilles Iacazio, Thierry Tron, M. Paula Robalo, Lígia O. Martins
