Fungi outcompete bacteria under increased uranium concentration in culture media.

As a key part of water management at the Ranger Uranium Mine (Northern Territory, Australia), stockpile (ore and waste) runoff water was applied to natural woodland on the mine lease in accordance with regulatory requirements. Consequently, the soil in these Land Application Areas (LAAs) presents a range of uranium concentrations. Soil samples were collected from LAAs with different concentrations of uranium and extracts were plated onto LB media containing no (0 ppm), low (3 ppm), medium (250 ppm), high (600 ppm) and very high (1500 ppm) uranium concentrations. These concentrations were similar to the range of measured uranium concentrations in the LAAs soils. Bacteria grew on all plates except for the very high uranium concentrations, where only fungi were recovered. Identifications based on bacterial 16S rRNA sequence analysis showed that the dominant cultivable bacteria belonged to the genus Bacillus. Members of the genera Paenibacillus, Lysinibacillus, Klebsiella, Microbacterium and Chryseobacterium were also isolated from the LAAs soil samples. Fungi were identified by sequence analysis of the intergenic spacer region, and members of the genera Aspergillus, Cryptococcus, Penicillium and Curvularia were dominant on plates with very high uranium concentrations. Members of the Paecilomyces and Alternaria were also present but in lower numbers. These findings indicate that fungi can tolerate very high concentrations of uranium and are more resistant than bacteria. Bacteria and fungi isolated at the Ranger LAAs from soils with high concentrations of uranium may have uranium binding capability and hence the potential for uranium bioremediation.

[Study on biosorption of uranium by Rhodotorula glutinis].

Characteristic of uranium biosorption in water solution by Rhodotorula glutinis was investigated in the present study and the optimal pH for uranium adsorption was found to be 6-7. At the same time, maximum adsorption capacity of 149.4 mgU/(g dry cell) was identified, and Langmuir adsorption models can be used to simulate the isothermal biosorption process with high correlation coefficient of 0.99. According to Fourier transform infrared spectra, a new peak at wave number of 904 cm(-1), which can be assigned to the stretch vibration of UO2, was detected in the cell which was contacted by the uranium, indicated that uranium was really absorbed by Rhodotorula glutinis. Changes in the uranium-exposed yeast biomass were in the stretching vibrations of amino or hydroxyl groups, which shift from 3309 to 3287 cm(-1), and in the stretching vibrations of C--O band, which shift from 1068 to 1080 cm(-1), and these are all attributed to the important role that they may played in the binding of uranium. Hardly any changes can be found in the characteristic IR adsorbing peaks of protein at wave numbers of 1653, 1540 and 1237 cm(-1) before and after uranium adsorption, making it clear that the major component and the structure of the biomass remained intact. 96% of the absorbed uranium can be easily desorbed by 0.1 mol x L(-1) NaHCO3. Obviously, the application potential of this yeast in the uranium wastewater treatment was very wide and expansive, and more more work should be done to realize its industrial use.

Caulobacter crescentus as a whole-cell uranium biosensor.

We engineered a strain of the bacterium Caulobacter crescentus to fluoresce in the presence of micromolar levels of uranium at ambient temperatures when it is exposed to a hand-held UV lamp. Previous microarray experiments revealed that several Caulobacter genes are significantly upregulated in response to uranium but not in response to other heavy metals. We designated one of these genes urcA (for uranium response in caulobacter). We constructed a reporter that utilizes the urcA promoter to produce a UV-excitable green fluorescent protein in the presence of the uranyl cation, a soluble form of uranium. This reporter is specific for uranium and has little cross specificity for nitrate (<400 microM), lead (<150 microM), cadmium (<48 microM), or chromium (<41.6 microM). The uranium reporter construct was effective for discriminating contaminated groundwater samples (4.2 microM uranium) from uncontaminated groundwater samples (<0.1 microM uranium) collected at the Oak Ridge Field Research Center. In contrast to other uranium detection methodologies, the Caulobacter reporter strain can provide on-demand usability in the field; it requires minimal sample processing and no equipment other than a hand-held UV lamp, and it may be sprayed directly on soil, groundwater, or industrial surfaces.

Physicochemical and mineralogical characterization of soil-saprolite cores from a field research site, Tennessee.

Site characterization is an essential initial step in determining the feasibility of remedial alternatives at hazardous waste sites. Physicochemical and mineralogical characterization of U-contaminated soils in deeply weathered saprolite at Area 2 of the DOE Field Research Center (FRC) site, Oak Ridge, TN, was accomplished to examine the feasibility of bioremediation. Concentrations of U in soil-saprolite (up to 291 mg kg(-1) in oxalate-extractable U(o)) were closely related to low pH (ca. 4-5), high effective cation exchange capacity without Ca (64.7-83.2 cmol(c) kg(-1)), amorphous Mn content (up to 9910 mg kg(-1)), and the decreased presence of relative clay mineral contents in the bulk samples (i.e., illite 2.5-12 wt. %, average 32 wt. %). The pH of the fill material ranged from 7.0 to 10.5, whereas the pH of the saprolite ranged from 4.5 to 8. Uranium concentration was highest (about 300 mg kg(-1)) at around 6 m below land surface near the saprolite-fill interface. The pH of ground water at Area 2 tended to be between 6 and 7 with U concentrations of about 0.9 to 1.7 mg L(-1). These site specific characteristics of Area 2, which has lower U and nitrate contamination levels and more neutral ground water pH compared with FRC Areas 1 and 3 (ca. 5.5 and <4, respectively), indicate that with appropriate addition of electron donors and nutrients bioremediation of U by metal reducing microorganisms may be possible.