AbstractSoil microorganisms may respond to metal stress by a shift in microbial community from metal sensitive to metal resistant microorganisms. In this study microbes isolated from soils irrigated with wastewater from Ranger Uranium Mine in northern Australia were tested both for their resistance to uranium (U), and their community level responses to variations in soil U and physicochemical parameters. Microbes isolated from soil by culturing grew under different (field) concentrations of U added to culture media in the form of uranyl nitrate and fungi out-competed the bacteria in media with very high U concentrations. However, this shift from bacteria to fungi that occurred in culture was not observed in soils with very high U concentrations under field conditions. This suggests that the U present in the field may be less bioavailable than U added to the culture media. Moreover, there was no difference in the cultured microbial community isolated from soils with different U concentrations which may be due to the fact that culturing technique captures only less than 1% of the soil microbial community. To explore this further, the soil microbial community was measured by culture-independent next generation sequencing using the 454 platform or pyrosequencing. One hundred and forty four soil samples were pyrosequenced and 183,317 bacterial V6 sequences were obtained.
Using pyrosequencing, the bacterial community in soil with background levels of U was different from those in soil with elevated U. Indicator species analysis showed that bacterial OTUs closely related to members of Kitasatospora, Sphingobacteria, Candidate_division_WS3 and Rhodobium were only present at medium, high and very high U sites during all the sampling times. A significant seasonal and temporal change in bacterial community was also measured as a result of seasonal and temporal change in soil U and other physicochemical variables. Uranium resistant microbes isolated in this study could be used to study resistance mechanisms and bioremediation potential. Furthermore, bacterial species associated with higher U concentrations may serve as useful indicators of U contamination in the wet-dry tropics.
|Date of Award||Aug 2013|
|Supervisor||Karen Gibb (Supervisor), David Parry (Supervisor) & Keith Mcguinness (Supervisor)|