Production and molecular characterization of enzymes related with the decolourisation ability of synthetic reactive dyes by yeast strains

Abstract

The present research work focused on the decolourisation of reactive dyes mediated by yeast. It comprises the decolourisation of the dyes Remazol Black B-A, Remazol Yellow RR, Levafix Blue CA, Levafix Red CA, Everzol Yellow, Sumifix Yellow, Sumifix Red, Everzol Red, Samofix Black, Navy Everzol ED, Sumifix Blue ESC, Sumifix Blue and Everzol Blue LED, mediated individually by yeast strains LIIIST7 (Candida tropicalis), LIVST11 (Saccharomycete sp), HOMOGS20 (Candida parapsilosis), HOMOGST27 (Yarrowia lipolytica), HOMOGST27A (Yarrowia lipolytica), LIIIS36 (Candida pseudoglaebosa) isolated from wastewater treatment plant and strain HOMOGST31 (Kluyveromyces marxianus) isolated from cheese. The strains were morphologically characterized in PDA and species identification was performed by molecular biology methods using both ITS (ITS 4 – ITS 5) and 26S rDNA (NL 1 – NL 4) set of primers. Colour reduction was assessed in Normal Solid Decolourisation Media NSDM and Normal Decolourisation Media NDM supplied with individual dyes and also with a mix of most of the dyes. The strains exhibited different processes of decolourisation, which occurred through mechanisms of biosorption (colourful yeast cells pellet) or through true decolourisation mechanisms. The presence of colourless yeast cell pellet associated with supernatant reduction of colour indicates an underlying biodegradation mechanism. LIIIS36 strain exhibited high tolerance and decolourisation capacity in solid media and the highest efficiency in decolourisation for all the dyes tested in a period of time ranging between 12 – 24 h. Enzymatic activities of manganese peroxidase (MnP), azoreductase, oxidoreductase and laccase were detected for LIIIS36, with the reductase activity being the most relevant. The intracellular extract was used to perform protein separation trough FPLC, which allowed the purification of protein fractions that afterwards showed oxidoreductase activity. Phytotoxicity response for the decolourisation products from LIIIS36 cultures was performed using a Trifolium pratense assay resulting in the effective concentration (EC) similar both for the decolourisation supernatant and the supernatant of yeast growth without dyes. Candida pseudoglaebosa LIIIS36 has revealed important traits which make it a promising strain for a yeast-based biological decolourisation process for reactive dyes.

Date of Award	19 Jul 2016
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Maria Manuela Pintado (Supervisor), Patrícia Moreira (Co-Supervisor) & Paula M. L. Castro (Co-Supervisor)