Characterization of Azo Reduction Activity in a Novel Ascomycete Yeast Strain

Abstract

Several model azo dyes are reductively cleaved by growing cultures of an ascomycete yeast species, Issatchenkia occidentalis. In liquid media containing 0.2 mM dye and 2% glucose in a mineral salts base, more than 80% of the dyes are removed in 15 h, essentially under microaerophilic conditions. Under anoxic conditions, decolorization does not occur, even in the presence of pregrown cells. Kinetic assays of azo reduction activities in quasi-resting cells demonstrated the following: (i) while the optimum pH depends on dye structure, the optimum pH range was observed in the acidic range; (ii) the maximum decolorizing activity occurs in the late exponential phase; and (iii) the temperature profile approaches the typical bell-shaped curve. These results indirectly suggest the involvement of an enzyme activity in azo dye reduction. The decolorizing activity of I. occidentalis is still observed, although at a lower level, when the cells switch to aerobic respiration at the expense of ethanol after glucose exhaustion in the culture medium. Decolorization ceased when all the ethanol was consumed; this observation, along with other lines of evidence, suggests that azo dye reduction depends on cell growth. Anthraquinone-2-sulfonate, a redox mediator, enhances the reduction rates of the N,N-dimethylaniline-based dyes and reduces those of the 2-naphthol-based dyes, an effect which seems to be compatible with a thermodynamic factor. The dye reduction products were tested as carbon and nitrogen sources. 1-Amino-2-naphthol was used as a carbon and nitrogen source, and N,N-dimethyl-p-phenylenediamine was used only as a nitrogen source. Sulfanilic and metanilic acids did not support growth either as a carbon or nitrogen source.Over the last two decades, considerable work has been done with the goal of using microorganisms as bioremediation agents in the treatment of wastewater containing textile dyes. These contaminants contribute a minor fraction to the usually high load of dissolved organic matter in textile effluents (35), but they are highly visible and must be removed in order to comply with the regulations concerning effluent discharge.Azo aromatic dyes are the major group of textile dyestuffs. These structures can be reductively cleaved into colorless amines by several bacterial species (for reviews, see references 2, 9, 41, and 43); nevertheless, azo dye reduction occurring in the presence of living matter can be an abiotic process. An example of this is the reduction of acid orange 7 (called dye IV in the present study) and reactive red 2 in anaerobic sludge, where sulfide, produced by sulfate-reducing microorganisms, can reduce azo bonds (45). In most of the reported processes of azo dye bioreduction, however, the participation of an enzymatic activity is assumed. Since the products of azo dye reduction, with few exceptions (4,11,26), cannot be used by bacteria as carbon and energy sources, the cleavage of azo bonds is a gratuitous process which can occur when the microorganisms use a reduced carbon compound as the gro...

Biodegradation of Methyl Red by Staphylococcus aureus Isolated from Waste Dump Site

“…1b) and 66.07-59.04% in 750 mL dilution between 3-12 days incubation period under aerobic condition. Similar results were reported on biodegradation of azo dyes by yeast (Issatchenkia occidentalis), where maximum decolourization was observed under aerobic conditions (Ramalho et al, 2004). They further reported that under anoxic condition decolourization was lesser due to absence of metabolic activities.…”

Aerobic decolorization of azo dye orange g by a new yeast isolate Candida cylindracea SJL6

“…The modified Normal Decolorization Medium (NDM) was used for the experiments, which consisted of (%): yeast extract, 0.25; KH 2 PO 4 , 0.5; MgSO 4 ·7H 2 O, 0.05; CaCl 2 ·2H 2 O, 0.013; and glucose, 2 (RAMALHO et al, 2004). After sterilization at 121 °C for 20 min, Orange G was added to the medium at different concentrations (100, 200, 300, 400, and 500 ppm).…”

Textile azo dye degradation by Candida rugosa INCQS 71011 isolated from a non-impacted area in Semi-Arid Region of Brazilian Northeast

“…Little is known about the degradation of dyes and color removal by yeasts (Singh, 2006); nonetheless, most studies show positive results. Several genera of yeast have been studied such as Kluyveromyces, Schizosaccharomyces, Issatchenkia, Debaryomyces, Pseudozyma, and Saccharomyces (Aksu and Dönmez, 2003;Ramalho et al, 2004;Yang et al, 2003Yang et al, , 2005Yu and Wen, 2005;Kumari and Abraham, 2007). Candida species have been used in some works and good results were presented for removal of reactive dyes in concentrations ranging from 10 -700 mg l -1 , nevertheless, these studies showed adsorption, besides degradation (Gönen and Aksu, 2009;Ertugrul et al, 2009) and absorption (Dönmez, 2002;Aksu and Dönmez, 2003).…”