Effects of selected physical and chemical parameters on uranium uptake by the bacterium Chryseomonas MGF-48

The effect of selected physical and chemical parameters, including media composition, uranium concentration, and metabolic inhibitors, on uranium uptake from aqueous solution by Chryseomonas sp. MGF-48, a bacterium isolated from electroplating effluent, was analysed. It was found that 198 mg/g (dry weight) of uranium was taken up from a 150 ppm (mg/l) solution of uranium when cells were maintained under starvation conditions. Uranium was released from the cells by addition of sodium carbonate. Uptake of uranium was reduced when cells were subjected to pretreatment with ultraviolet (u.v.) light (263.7 nm, 10 min) or heat (100 degreesC, 15 min), i.e., 99.8 and 57.5 mg/g, respectively. Addition of 2, 4-dinitrophenol (10 mM) or sodium azide (0.1%) resulted in decreased uptake (129 and 123 mg/g, respectively), whereas addition of glycerol-2-phosphate (G-2-P) resulted in deposition of uranium. Maximum uptake of uranium occurred at pH 6.5. Uranium uptake in the presence of selected carbohydrates decreased as follows: xylose > arabinose > mannose > maltose > glucose. When Chryseomonas sp. MGF-48 was exposed to 5, 50, or 100 mg/l uranium prior to uptake experiments, a decrease in uranium uptake was noted. Furthermore, immobilization of the bacterial cells in a calcium-alginate medium reduced the efficiency of uptake, yielding only 60% uranium uptake. It is concluded that uranium uptake and accumulation by this bacterium involves both metabolism-independent absorption and metabolism-dependent absorption, the former being considered to be more efficient.