1. One hundred thirty yeasts were isolated from effluents waste waters of different industries of Pakistan. These indigenous isolates showed resistance to heavy metals like Cr+6, Cd+2, Pb+2, Cu+2, Hg+2, Zn+2, Ni+2+, and Co+2.
2. Pb+2 was found to be the least toxic metal while Hg+2, was the most toxic metal to the yeast isolated from industrial effluents. CMBL112 showed MIC value 5mg/ml for lead. The maximum resistance 2.5mg/ml for Cr+6 was observed in CMBLY4, 32,33,42,46,62,80, and 112. Among the yeast isolates tested, CMBLY30, 31,32,37,52,58,62,64,99,100,121 and 125 showed very high degrees of resistance to the Cd+2, MIC values ranging from 2.0-2.5mg/ml of Cd+2 in YEPD medium.
3. Growth conditions of the isolates wee worked out in order to get maximum growth of the yeast biomass. Most of the isolates showed optimum growth at 30oC(CMBLY 1,3,56,57, and 80) while a few (CMBLY 37,109and 115) showed maximum growth at 25oC. The optimum temperature for CMBLY5, 10,40,64,70,101,102 and 106 was 35oC.
4. For most of the yeast isolates better growth was obtained in slightly acidic medium, while CMBLY1,37,51,57,80 and 102 showed maximum growth at neutral pH.
5. The growth of the yeast isolates was delayed and cell size became smaller in the presence of heavy metals Cr+2, Cd+2 and Pb+2.
6. Majority of the yeasts isolated from industrial effluence were Rhodotorula sp., Saccharmoyces cerevisia, Candida sp. and Pichia sp. On the basis of physiological, morphological and biochemical studies other isolates were identified as Kluyveromyces, Debaromyces yamadae, Hanseniaspora osmophila and Williopsis saturnus.
7. The yeast isolates were excellent absorbers of chromium from the YEPD medim as well as water, CMBLY1,3 and 31 showed >90% reduction in the amount of Cr+6 in the YEPD medium after 96 hours incubation. CMBLY 1 and 32 removed 18% and 12% of the of chromium from the water after one hour with an initial concentration of 100µg/ml.
8. After 96 hours of incubation r education in the concentration of copper was 92% by CMBLY124 was found to be a good absorber of copper from the aqueous solution as it accumulated 19.3 mg of Cu+2/g wet biomass. CMBLY37 was found to be the most different isolate capable of accumulating 32 mg of copper/ g of yeast.
9. CMBLY5, 8, 37,51,102 and 112 reduced lead from the YEPD agar medium significantly. The decrease in Pb+2 concentration in YEPD broth was more than 50% after 96 hours incubation. CMBLY5, 37 and 51 were the best among the yeast isolates for removal of Pb+2 from water.
10. CMBLY14, 57, 64 and 12 could reduce 80% of Cd+2 from the YEPD medium after 96 hours of incubation. The highest removal was done by CMBLY14 (90%) followed by CMBLY57 (89%), 64(86%), 64(86%) and 121(84%). The yeast isolates could also remove cadmium from the aqueous salutation CMBLY121 could remove 17.36mg of cadmium /g of yeast biomass, whereas CMBLY64 and 32 removed 16.8 and 143.2 mg of Cd+2/g of yeast biomass from aqueous solutions.
11. PAGE of the yeast isolates showed that with the addition of metals new proteins were induced. Moreover, certain proteins were suppressed as a results of metal stress. Protein response of the yeast isolates was metal as well as isolate specific.