Evaluation of the involvement of Basidiomycetous yeast cell wall during azo-dye biodecolorization.

HIPÓLITO F. PAJOT; JULIA I. FARIÑA; LUCÍA I.C. DE FIGUEROA

Oropesa del Mar

Simposio; XXIV International Specialized Symposium on Yeasts.; 2005

International Commission on Yeasts

Effluent discharge from textile and dyestuff industries is a cause of health concern and its disposal into receiving waters irreversibly damages the environment. For this reason, dye degradation has become a research topic receiving great attention in water-pollution control. Microbial treatment of effluents is nowadays seen as a cost-effective method being considered as a promising and ‘eco-friendly’ alternative to conventional physico-chemical techniques. In contrast to the anaerobic bacterial processes which may lead to carcinogenic aromatic amines, those involving fungal ligninolytic enzymes with low substrate-specificity are suitable for aerobic dye degradation avoiding hazardous product formation. The aim of this study was to investigate the ability of several yeasts isolated from the “Yungas Rainforest” (Tucumán location, Argentina) to decolorize several commercial azo-dyes. Starting with 65 yeast isolates, at the end of the screening program 5 yeasts were selected for their high decolorizing ability. Biochemical and physiological tests and molecular analysis revealed that these yeasts belonged to the Trichosporon genus (Basidiomycetous yeasts) and could be classified in 2 different specie. These yeasts were further subjected to decolourization assays in liquid media containing a final concentration of 200 mg/L of either Vilmafix Blue RR-BB or Vilmafix Red 7B-HE, and the kinetics of dye disappearance were evaluated. After 72 h, the extent of colour removal reached 89 and 93%, for the 2 different groups. Throughout decolourization, UV-visible spectra of culture supernatants were recorded and spectra comparisons at 12, 36 and 72 h of incubation were performed. These studies confirmed the almost complete decolourization after 36 h of cultivation. Negative, heat-killed yeast controls showed only partial decolourization indicating that cell wall participation, e.g. for bioaccumulation, would not be the main implicated mechanism. Scanning electron-photomicrography showed slight cell surface differences between dye- and non-dye-exposed yeasts, thus suggesting a major participation of enzymatic processes during azo-dye decolourization. These results are highly promising and demonstrate the huge potential of the selected Basidiomycetous yeasts for the ecological treatment of dye-containing effluents.