الفهرس 
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Abstract
40% (v/v).
6- Cell concentrations varied among the selected yeast strains. In case of methyl red dye, C. sphaerica, Cry. albidus , C. utilis(1),and Rho. rubra, the optimal OD for the decolorization of the dye was at 0.3,whereas, the optimum OD of Rho. glutinis and S. cerevisiae(43) was at 0.1 but S. cerevisiae(44) and Cry. uniguttulatus was at 0.5 and 0.7 OD, respectively. In case of reactive brilliant blue dye, the optimal OD for decolorization by Cry. albidus and C. utilis(1) was at 0.3, whereas, the optimum OD of Rho. glutinis, Rho. rubra and C. sphaerica was at 0.1, 0.5 and 0.7 OD, respectively. In case of malachite green dye, the optimal OD for decolorization by C. utilis(3) and Cry. albidus was at 0.3, whereas, the optimum OD of Rho. rubra and S. cerevisiae(44) was at 0.5 ,but Cry. uniguttulatus was at 0.7 OD.
7- The maximum decolorization rate was observed at a concentration of 10 mg /l of methyl red and reactive brilliant blue dyes by all the selected yeast strains. However, the maximum decolorization of malachite green dye was observed at a concentration of 1 mg /l for all the selected yeast strains.
8- The high decolorization rate of methyl red, reactive brilliant blue and malachite green dyes achieved in a medium containing glucose as a best carbon source. However, the best nitrogen source for the decolorization of methyl red and reactive brilliant blue dyes was
yeast extract, but it isn’t true in case of malachite green dye, NaNO3 and NH4NO3 were the best nitrogen sources.
9- The highest biodegradation of methyl red and reactive brilliant blue dyes by the selected yeast strains was confirmed by using distilled water as a decolorization medium. While, the biodegradation of malachite green dye was confirmed by using distilled water with 5% glucose as a decolorization medium.
According to the potentiality of yeast strains; C. sphaerica could achieved a removal ratio of 78.94%, while S. cerevisiae(44) 78.01%, S. cerevisiae(43) 75.14%, Cry. albidus 73.16%, Rho. glutinis 73.1%, Cry. uniguttulatus 72.74%, Rho. rubra 70.82% and C. utilis(1) 70.1% in case of methyl red dye. However, in case of reactive brilliant blue dye,
C. sphaerica could achieved a removal ratio of 68.83%, C. albidus 68.40%, Rho. rubra 67.75%, Rho. glutinis 66.88% and C. utilis(1) 63.85%. Whereas, the use of malachite green dye, S. cerevisiae(44)could achieved a removal ratio of 76.21% , Cry. uniguttulatus72.48%, C. utilis(3) 70.26%, Cry. albidus 68.74%, Rho. rubra 67.49 % and Rho. glutinis 62.66 %.
Induction in the enzymatic activities of laccase, tyrosinase and lignin peroxidase indicates the involvement of these enzymes for the decolorization of the three used dyes. Laccase is highly activated for the biodegradation of the three dyes except C. utilis(1) followed by lignin peroxidase and tyrosinase enzymes, respectively. In the
biodegradation of methyl red dye by C. utilis(1), lignin peroxidase is highly activated then tyrosinase enzyme
The FTIR spectrum of extracted metabolites of the studied three dyes after decolorization showed significant changes in the position of peaks, appearance of new peaks and disappearance of some peaks. This confirmed the change in the chemical composition of the studied dyes.
The phytotoxicity results of the three studied dyes with grains of Sorghum versicolor and seeds of Phaseolus vulgaris showed more sensitivity towards the three dyes, while the products obtained after decolorization in the presence of a mixture of the most potent yeast strains have less inhibitor effects on seedling growth in comparing with the control.