Multiple metal tolerance and biosorption of cadmium by Candida tropicalis isolated from industrial effluents: glutathione as detoxifying agent.

The ability of cadmium uptake by metal-resistant yeast, Candida tropicalis, from the liquid medium and wastewater was evaluated. The minimum inhibitory concentration of Cd(2+) against C. tropicalis was 2,500 mg L(-1). The yeast also showed tolerance toward Zn(2+) (1,400 mg L(-1)), Ni(2+) (1,000 mg L(-1)), Hg(2+) (1,400 mg L(-1)), Cu(2+) (1,000 mg L(-1)), Cr(6+) (1,200 mg L(-1)), and Pb(2+) (1,000 mg L(-1)). The yeast isolate showed typical growth curves, but lag and log phases extended in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 8. The metal processing ability of the isolate was determined in a medium containing 100 mg L(-1) of Cd(2+). C. tropicalis could decline Cd(2+) 70%, 85%, and 92% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd(2+) 40% and 78% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and nonprotein thiol levels by 135% and 134% at 100-mg L(-1) concentration, respectively. An increase in the synthesis of GSH is involved in metal tolerance, and the presence of increasing GSH concentrations may be a marker for high metal stress in C. tropicalis. C. tropicalis, which is resistant to heavy metal ions and is adaptable to the local environmental conditions, may be employed for metal detoxification operations.