Wasteful Azo Dyes as a Source of Biologically Active Building Blocks

Ana Fernandes, Bruna Pinto, Lorenzo Bonardo, Beatriz Royo, M. Paula Robalo, Lígia O. Martins

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


In this work, an environment-friendly enzymatic strategy was developed for the valorisation of dye-containing wastewaters. We set up biocatalytic processes for the conversion of azo dyes representative of the main classes used in the textile industry into valuable aromatic compounds: aromatic amines, phenoxazinones, phenazines, and naphthoquinones. First, purified preparations of PpAzoR azoreductase efficiently reduced mordant, acid, reactive, and direct azo dyes into aromatic amines, and CotA-laccase oxidised these compounds into phenazines, phenoxazinones, and naphthoquinones. Second, whole cells containing the overproduced enzymes were utilised in the two-step enzymatic conversion of the model mordant black 9 dye into sodium 2-amino-3-oxo-3H-phenoxazine-8-sulphonate, allowing to overcome the drawbacks associated with the use of expensive purified enzymes, co-factors, or exquisite reaction conditions. Third, cells immobilised in sodium alginate allowed recycling the biocatalysts and achieving very good to excellent final phenoxazine product yields (up to 80%) in water and with less impurities in the final reaction mixtures. Finally, one-pot systems using recycled immobilised cells co-producing both enzymes resulted in the highest phenoxazinone yields (90%) through the sequential use of static and stirring conditions, controlling the oxygenation of reaction mixtures and the successive activity of azoreductase (anaerobic) and laccase (aerobic).

Original languageEnglish
Article number672436
JournalFrontiers in Bioengineering and Biotechnology
Publication statusPublished - 15 Jun 2021


  • aromatic amines
  • azoreductase
  • laccases
  • phenazines
  • phenoxazinones
  • whole-cell catalysis


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