Study for optimization of Uranium absorption by new bacterium MGF-48

The mechanisms of uranium uptake from aqueous solution by pseudomonas sp. MGF-48 which was isolated from electroplating effluent of a metal factory in the south of Tehran (8,9) and the effects of growth conditions, media, concentration of uranium and the effect of metabolic inhibitors were studied. A maximum of 198 mg/g (dry weight) of uranium was taken up from a solution of 150 ppm, under starvation conditions (16 h, no energy source), indicating metabolism-independent adsorption. The uranium was released from the cells by addition of sodium carbonate. Uptake was reduced by pretreatment with UV (263.7 nm, 2 h), and by heat (100 degree C, 15 min) to 99.8 and 57.5 mg/g respectively. The relationship of uptake to metabolic activity was examined. Presence of 2,4-dinitrophenol (10 mM) or sodium azide (0.1 %) resulted in decreased uptake (129, and 123 mg/g respectively). Also addition of G-2-p (glycerol 2-phosphate) and uranium simultaneously resulted in phosphatase activity and deposition of uranium crystals on the surface. Maximum uptake was observed at PH 6.5-6.8. Uranium uptake in the presence of various sugars decreased in order Xylose> Arabinose> Mannose> Maltose> Glucose. When the bacteria was exposed to lower concentrations of uranium (5,50 or 100 ppm) in advance, uranium uptake from the solution of 150 ppm decreased to 127 mg/g dry weight which mean that no adaptation has occurred. Immobilization of the cells in Ca-alginate reduced the removal efficiency and only 60% of uranium was taken up from the above solution. The results indicate that uranium accumulation involves metabolism dependent absorption, the former being more efficient. Immobilized cells in Ca-alginate showed significant decrease in uranium removal efficiency compared to free cells. (author)