Uranium(VI) reduction by Anaeromyxobacter dehalogenans strain 2CP-C.
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Previous studies demonstrated growth of Anaeromyxobacter dehalogenans strain 2CP-C with acetate or hydrogen as the electron donor and Fe(III), nitrate, nitrite, fumarate, oxygen, or ortho-substituted halophenols as electron acceptors. In this study, we explored and characterized U(VI) reduction by strain 2CP-C. Cell suspensions of fumarate-grown 2CP-C cells reduced U(VI) to U(IV). More-detailed growth studies demonstrated that hydrogen was the required electron donor for U(VI) reduction and could not be replaced by acetate. The addition of nitrate to U(VI)-reducing cultures resulted in a transitory increase in U(VI) concentration, apparently caused by the reoxidation of reduced U(IV), but U(VI) reduction resumed following the consumption of N-oxyanions. Inhibition of U(VI) reduction occurred in cultures amended with Fe(III) citrate, or citrate. In the presence of amorphous Fe(III) oxide, U(VI) reduction proceeded to completion but the U(VI) reduction rates decreased threefold compared to control cultures. Fumarate and 2-chlorophenol had no inhibitory effects on U(VI) reduction, and both electron acceptors were consumed concomitantly with U(VI). Since cocontaminants (e.g., nitrate, halogenated compounds) and bioavailable ferric iron are often encountered at uranium-impacted sites, the metabolic versatility makes Anaeromyxobacter dehalogenans a promising model organism for studying the complex interaction of multiple electron acceptors in U(VI) reduction and immobilization. (+info)
Application of a high-density oligonucleotide microarray approach to study bacterial population dynamics during uranium reduction and reoxidation.
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Reduction of soluble uranium U(VI) to less-soluble uranium U(IV) is a promising approach to minimize migration from contaminated aquifers. It is generally assumed that, under constant reducing conditions, U(IV) is stable and immobile; however, in a previous study, we documented reoxidation of U(IV) under continuous reducing conditions (Wan et al., Environ. Sci. Technol. 2005, 39:6162-6169). To determine if changes in microbial community composition were a factor in U(IV) reoxidation, we employed a high-density phylogenetic DNA microarray (16S microarray) containing 500,000 probes to monitor changes in bacterial populations during this remediation process. Comparison of the 16S microarray with clone libraries demonstrated successful detection and classification of most clone groups. Analysis of the most dynamic groups of 16S rRNA gene amplicons detected by the 16S microarray identified five clusters of bacterial subfamilies responding in a similar manner. This approach demonstrated that amplicons of known metal-reducing bacteria such as Geothrix fermentans (confirmed by quantitative PCR) and those within the Geobacteraceae were abundant during U(VI) reduction and did not decline during the U(IV) reoxidation phase. Significantly, it appears that the observed reoxidation of uranium under reducing conditions occurred despite elevated microbial activity and the consistent presence of metal-reducing bacteria. High-density phylogenetic microarrays constitute a powerful tool, enabling the detection and monitoring of a substantial portion of the microbial population in a routine, accurate, and reproducible manner. (+info)
A catalytic beacon sensor for uranium with parts-per-trillion sensitivity and millionfold selectivity.
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Here, we report a catalytic beacon sensor for uranyl (UO2(2+)) based on an in vitro-selected UO2(2+)-specific DNAzyme. The sensor consists of a DNA enzyme strand with a 3' quencher and a DNA substrate with a ribonucleotide adenosine (rA) in the middle and a fluorophore and a quencher at the 5' and 3' ends, respectively. The presence of UO2(2+) causes catalytic cleavage of the DNA substrate strand at the rA position and release of the fluorophore and thus dramatic increase of fluorescence intensity. The sensor has a detection limit of 11 parts per trillion (45 pM), a dynamic range up to 400 nM, and selectivity of >1-million-fold over other metal ions. The most interfering metal ion, Th(IV), interacts with the fluorescein fluorophore, causing slightly enhanced fluorescence intensity, with an apparent dissociation constant of approximately 230 microM. This sensor rivals the most sensitive analytical instruments for uranium detection, and its application in detecting uranium in contaminated soil samples is also demonstrated. This work shows that simple, cost-effective, and portable metal sensors can be obtained with similar sensitivity and selectivity as much more expensive and sophisticated analytical instruments. Such a sensor will play an important role in environmental remediation of radionuclides such as uranium. (+info)
Determination of uranium, thorium and potassium activity concentrations in soil cores in Araba valley, Jordan.
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Soil samples were collected from six different locations in Araba valley, situated between Aqaba port and Dead sea. The samples have been analysed by using gamma-ray spectrometry. From the measured gamma-ray spectra, activity concentrations are determined for (238)U, (232)Th and (40)K. The mean activity concentration for (238)U, (232)Th and (40)K was found to be in the range 19 +/- 1.4 to 38.7 +/- 3, 14.3 +/- 0.8 to 35 +/- 3.2 and 94 +/- 18.9 to 762 +/- 47.4 Bq kg(-1), respectively. These results indicate that the mean concentrations of (238)U, (232)Th and (40)K in the populated Araba valley are lower than those in other populated areas. On the other hand, the concentrations of the major oxides (Al(2)O(3), SiO(2), K(2)O, CaO and Fe(2)O(3)) in the samples were determined using wavelength dispersive X-ray fluorescence. High potassium and iron content in some samples might be attributed to the active faults, which refer to the Dead sea transform fault. (+info)
Streptomyces radiopugnans sp. nov., a radiation-resistant actinomycete isolated from radiation-polluted soil in China.
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The taxonomic position of an actinomycete isolated from radiation-polluted soil collected in Xinjiang Province, north-west China, was determined by using a polyphasic approach. The isolate, designated strain R97T, had chemical and morphological properties characteristic of streptomycetes. An almost-complete 16S rRNA gene sequence of the isolate was generated and compared with corresponding sequences of representative streptomycetes. The 16S rRNA data not only supported the classification of the strain in the genus Streptomyces but also showed that it represented a distinct phyletic line that was most closely, albeit loosely, associated with three other thermotolerant organisms, namely Streptomyces macrosporus NBRC 14748T, Streptomyces megasporus NBRC 14749T and Streptomyces thermolineatus NBRC 14750T. Strain R97T could be distinguished from these organisms based on a range of phenotypic properties. It is proposed that R97T (=CGMCC 4.3519T=DSM 41901T) be classified as the type strain of a novel species in the genus Streptomyces, Streptomyces radiopugnans sp. nov. The organism was shown to be resistant to 60Co gamma radiation at a dose of 15 kGy. (+info)
Lechevalieria xinjiangensis sp. nov., a novel actinomycete isolated from radiation-polluted soil in China.
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A novel actinomycete was isolated from radiation-polluted soil collected from Xinjiang in north-western China. The isolate, strain R24(T), was found to have chemical and morphological properties associated with members of the genus Lechevalieria. An almost-complete 16S rRNA gene sequence of the isolate was aligned with corresponding sequences from representatives of the genus Lechevalieria and related taxa, using three tree-making algorithms, and was shown to form a distinct phyletic line in the Lechevalieria phylogenetic tree. DNA-DNA relatedness and phenotypic data served to distinguish strain R24(T) from members of the three Lechevalieria species with validly published names. The genotypic and phenotypic data show that the isolate should be classified as a novel species within the genus Lechevalieria. The name proposed for this taxon is Lechevalieria xinjiangensis sp. nov. The type strain is R24(T) (=CGMCC 4.3525(T)=DSM 45081(T)). (+info)
Estimating terrestrial uranium and thorium by antineutrino flux measurements.
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Exposure from the Chernobyl accident had adverse effects on erythrocytes, leukocytes, and, platelets in children in the Narodichesky region, Ukraine: a 6-year follow-up study.
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