Enzymatic biotransformation of the azo dye Sudan Orange G with bacterial CotA-laccase

J Biotechnol. 2009 Jan 1;139(1):68-77. doi: 10.1016/j.jbiotec.2008.09.001. Epub 2008 Sep 25.


In the present study we show that recombinant bacterial CotA-laccase from Bacillus subtilis is able to decolourise, at alkaline pH and in the absence of redox mediators, a variety of structurally different synthetic dyes. The enzymatic biotransformation of the azo dye Sudan Orange G (SOG) was addressed in more detail following a multidisciplinary approach. Biotransformation proceeds in a broad span of temperatures (30-80 degrees C) and more than 98% of Sudan Orange G is decolourised within 7h by using 1 U mL(-1) of CotA-laccase at 37 degrees C. The bell-shape pH profile of the enzyme with an optimum at 8, is in agreement with the pH dependence of the dye oxidation imposed by its acid-basic behavior as measured by potentiometric and electrochemical experiments. Seven biotransformation products were identified using high-performance liquid chromatography and mass spectrometry and a mechanistic pathway for the azo dye conversion by CotA-laccase is proposed. The enzymatic oxidation of the Sudan Orange G results in the production of oligomers and, possibly polymers, through radical coupling reactions. A bioassay based on inhibitory effects over the growth of Saccharomyces cerevisiae shows that the enzymatic bioremediation process reduces 3-fold the toxicity of Sudan Orange G.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Azo Compounds / chemistry
  • Azo Compounds / metabolism*
  • Azo Compounds / pharmacology
  • Bacillus subtilis / enzymology*
  • Bacillus subtilis / genetics
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Biological Assay
  • Biotransformation
  • Chromatography, High Pressure Liquid
  • Coloring Agents / metabolism
  • Electrochemistry
  • Hydrogen-Ion Concentration
  • Kinetics
  • Laccase / genetics
  • Laccase / metabolism*
  • Mass Spectrometry
  • Models, Chemical
  • Nonlinear Dynamics
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Saccharomyces cerevisiae / drug effects
  • Saccharomyces cerevisiae / growth & development
  • Spectrophotometry
  • Temperature


  • Azo Compounds
  • Bacterial Proteins
  • Coloring Agents
  • Recombinant Proteins
  • Orange G
  • Laccase