الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
Fifty yeast isolates from different habitats in Menoufia governorate Egypt, were screened for their ability to decolorize the azo dyes, Direct Red 81 (DR81) and Reactive Brilliant Red X-3B (RBR). Out of those, twenty two isolates displayed positive results therefore they were characterized morphologically and physiologically. The most active two isolates were identified as Meyerozyma guilliermondii and Naganishia diffluens on the bases of 28S ribosomal RNA sequencing. The dyes decolorization percentage of 0.015 and0.005% of DR81 and RBR reached 88.7 and 81.3% by these two yeasts respectively. Sucrose and glucose were the best carbon sources for the two yeasts whereas peptone was the culture was nfor 48h of shake Ċ030 urce for both. Incubation at best nitrogen sothe best physical conditions for bio-decolorization process. The results also indicated that pH5 and 7 are the optimum pH values; increasing the concentration of NaCl resulted in a significant decreasing in dye decolorization. Elevated erse effect on the ability had a significant div (100 ppm) 4Soconcentrations of Cuof N. diffluens to decolorize RBR. On the other hand, there was a non-significant towards uilliermondiig M. fon the activity o 3Cland Fe 4Soeffect of Cuzation of showed no effect on decolori 2Cland also Co DR81ation of decolorizhad asignificant effect on decolorization of 2Cl20 ppm of Zn and 50 .both dyesRBR and DR81 respectively. The decolorization of the dyes was confirmed by UV-visible spectra and IR analysis. Direct red and reactive red dyes decolorization were attributed to biodegradation and biosorption. This study investigated the biosorption of Direct Red 81 and Reactive Brilliant Red X-3B dyes according to pH, biomass dosage, contact time and dye concentration by M. guilliermondii and N. diffluens. The highest biosorption capacity of both dyes was ptimum O. Ċ0incubation using shaker incubator at 28 reached after 10 mindecolorization was observed at pH 2 and 0.02 % dye Conc for both dyes. Optimum decolorization of Direct Red 81 dye observed at 0.25 g\50ml of M. guilliermondii biomass dosage and decreased by increasing the dosage, while the optimum decolorization of Reactive Brilliant Red dye remained stable at 0.25 and 0.5 g\50ml of N. diffluens biomass dosage and decreased by increasing the dosage. These results were discussed in relation with their importance in the field of biotechnological application for bioremediation of azo dyes-polluted effluents.