Large numbers of synthetic dyes are used for various industrial applications and significant proportion appears in the form of wastewater and is spilled into the environment. These contaminated effluents which mainly are from dyeing and also finishing processes and are associated with the water pollution. Wastewater resulting from these shows improper impacts in terms of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), suspended solids, color, affect on pH and the organic compounds, [1] -[3] . Azo dyes may be classified as toxic and carcinogenic [4] . Synthetic dyes cannot be efficiently decolorized by traditional biological processes [5] . Thus, a number of biological and chemical methods have been developed for the efficient removal of industrial azo dyes [6] [7] .

Azo dyes are electron-deficient xenobiotic components because of their azo linkage, and also other electron- withdrawing groups, which generate an electron deficiency and make the dye less susceptible to biodegradation [8] [9] . However under the appropriate conditions, they can be degraded by reductases [10] - [12] . Azoreductases work only in the presence of reducing equivalents, e.g., FADH, NADH and NADPH [13] [14] . The available evidence indicates that azoreductase activity can be associated with more than one reductase [15] . Azoreductases are present in microorganisms, such as bacteria [16] - [18] , algae [19] and yeast [20] .

The use of microorganisms for the biodegradation of dyes is an attractive alternative to the development of bioremediation processes for the treatment of textile wastewater. Biological methods are environmentally friendly, produce less sludge than physical and chemical systems, and are relatively inexpensive, as the running cost is low. Microbial discoloration can occur via biosorption, enzymatic degradation or a combination of both [21] .

Yeast has long been known to be capable of bioaccumulation of heavy metal from solution and recently some reports for accumulation of dyes [22] - [30] . But little work has been carried out investigating the ability of yeast to act a biocatalyst for textile dyes especially using harvested cells.

This study aims to study the bioconversion potential of commonly available Saccharomyces cerevisiae yeast for the two textile dyes of Carmoisine and Reactive Black 5 at batch-scale level.

Harvested cells of S. cerevisiae were investigated in the reaction mixtures to study the ability for biotransformation of two synthetic dyes. A few dye bioconversions have been reported by this yeast. The results are given asthe units of percentage of biotransformation in Table 1. Figure 1 and Figure 2 show the decolorization of Carmoisine by S. cerevisiae. Figure 3 shows the decolorization of Reactive Black 5 (25 mg/l) and Figure 4 shows biotransformation of Carmoisine (50 mg/l) using different concentration of S. cerevisiae.

Initially different concentrations of cells (0.05% to 2.5%) were studied and it was found that by increasing the cell mass, more biotransformation happened. For main experiments the concentration of 1% was used. Decrease in the absorption indicates that decolourization of this dye occurred by degradation. Reactive Black 5 and Carmoisine are degraded by biotransformation 85% and 53% within 24 hours in water at the room temperature.

S. cerevisiae is capable of utilizing a variety of carbon and nitrogen sources. In the absence of natural carbon and nitrogen sources the yeast is able to use some other synthetic chemicals. In this investigation, an experiment protocol was designed and used to check the ability of Saccharomyces cerevisiae to utilize two textile dyes of

Carmoisine and Reactive Black 5 at batch-scale level. Microscopic and macroscopic observations showed that the dye decolourizations are due to microbial biotransformation and not due to biosorption.

Although some reports have mentioned that S. cerevisiae in cultures is able to accumulate some dyes in several days. Biotransformation of these dyes in this study proves that the harvested cells of the S. cerevisiae can be promising for further research and practical usage in the field of dye biotransformation for example in chemical, biological sciences and industries. As well hold promise in providing a low cost and efficient means to treat the textile effluent.