Soil uranium concentration at Ranger Uranium Mine Land Application Areas drives changes in the bacterial community.

Soil microorganisms may respond to metal stress by a shift in the microbial community from metal sensitive to metal resistant microorganisms. We assessed the bacterial community from low (2-20 mg kg-1), medium (200-400 mg kg-1), high (500-900 mg kg-1) and very high (>900 mg kg-1) uranium soils at Ranger Uranium Mine in northern Australia through pyrosequencing. Proteobacteria (28.85%) was the most abundant phylum at these sites, followed by Actinobacteria (9.31%), Acidobacteria (7.33%), Verrucomicrobia (2.11%), Firmicutes (2.02%), Chloroflexi (1.11%), Cyanobacteria (0.93%), Planctomycetes (0.82%), Bacteroidetes (0.46%) and Candidate_division_WS3 (Latescibacteria) (0.21%). However, 46.79% of bacteria were unclassified. Bacteria at low U soils differed from soils with elevated uranium. Bacterial OTUs closely related to Kitasatospora spp., Sphingobacteria spp. and Rhodobium spp. were only present at higher uranium concentrations and the bacterial community also changed with seasonal and temporal changes in soil uranium and physicochemical variables. This study using next generation sequencing in association with environmental variables at a uranium mine has laid a foundation for further studies of soil-microbe-metal interactions which may be useful for developing sustainable management and rehabilitation strategies. Furthermore, bacterial species associated with higher uranium may serve as useful indicators of uranium contamination in the wet-dry tropics.

Land application of mine water causes minimal uranium loss offsite in the wet-dry tropics: Ranger Uranium Mine, Northern Territory, Australia.

Ranger Uranium Mine (RUM) is situated in the wet-dry tropics of Northern Australia. Land application (irrigation) of stockpile (ore and waste) runoff water to natural woodland on the mine lease is a key part of water management at the mine. Consequently, the soil in these Land Application Areas (LAAs) presents a range of uranium (U) and other metals concentrations. Knowledge of seasonal and temporal changes in soil U and physicochemical parameters at RUM LAAs is important to develop suitable management and rehabilitation strategies. Therefore, soil samples were collected from low, medium, high and very high U sites at RUM LAAs for two consecutive years and the effect of time and season on soil physicochemical parameters particularly U and other major solutes applied in irrigation water was measured. Concentrations of some of the solutes applied in the irrigation water such as sulphur (S), iron (Fe) and calcium (Ca) showed significant seasonal and temporal changes. Soil S, Fe and Ca concentration decreased from year 1 to year 2 and from dry to wet seasons during both years. Soil U followed the same pattern except that we recorded an increase in soil U concentrations at most of the RUM LAAs after year 2 wet season compared to year 2 dry season. Thus, these sites did not show a considerable decrease in soil U concentration from year 1 to year 2. Sites which contained elevated U after wet season 2 also had higher moisture content which suggests that pooling of U containing rainwater at these sites may be responsible for elevated U. Thus, U may be redistributed within RUM LAAs due to surface water movement. The study also suggested that a decrease in U concentrations in LAA soils at very high U (>900 mg kg(-1)) sites is most likely due to transport of particulate matter bound U by surface runoff and U may not be lost from the surface soil due to vertical movement through the soil profile. Uranium attached to particulate matter may reduce its potential for environmental impact. These findings suggest that U is effectively adsorbed by the soils and thus land application may serve as a useful tool for U management in the wet-dry tropics of northern Australia.

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.