Bacterial community succession during in situ uranium bioremediation: spatial similarities along controlled flow paths

Abstract

Bacterial community succession was investigated in a field-scale subsurface reactor formed by a series of wells that received weekly ethanol additions to re-circulating groundwater. Ethanol additions stimulated denitrification, metal reduction, sulfate reduction and U(VI) reduction to sparingly soluble U(IV). Clone libraries of SSU rRNA gene sequences from groundwater samples enabled tracking of spatial and temporal changes over a 1.5-year period. Analyses showed that the communities changed in a manner consistent with geochemical variations that occurred along temporal and spatial scales. Canonical correspondence analysis revealed that the levels of nitrate, uranium, sulfide, sulfate and ethanol were strongly correlated with particular bacterial populations. As sulfate and U(VI) levels declined, sequences representative of sulfate reducers and metal reducers were detected at high levels. Ultimately, sequences associated with sulfate-reducing populations predominated, and sulfate levels declined as U(VI) remained at low levels. When engineering controls were compared with the population variation through canonical ordination, changes could be related to dissolved oxygen control and ethanol addition. The data also indicated that the indigenous populations responded differently to stimulation for bioreduction; however, the two biostimulated communities became more similar after different transitions in an idiosyncratic manner. The strong associations between particular environmental variables and certain populations provide insight into the establishment of practical and successful remediation strategies in radionuclidecontaminated environments with respect to engineering controls and microbial ecology.

How sulphate-reducing microorganisms cope with stress: lessons from systems biology

“…Analysis of the metagenome from the pristine area indicated the presence of sulphate-reducing deltaproteobacteria at low abundance, with the orders Desulfuromonadales and Myxococcales as the dominant deltaproteobacterial lineages. The elimination of nitrate stress by denitrification seemed to stimulate the growth of SRMs at the contaminated site 113,131,133,137,139 , in agreement with functional genomic studies that have shown that nitrate is a potent inhibitor of these organisms 39 . These results underscore the value of stress response analysis for improving the effective implementation of SRMs in biotechnological applications.…”

“…The local groundwater in the vicinity of the site contains one of the most concentrated mobile, subsurface uranium plumes in the United States. Numerous SRM species (particularly from the Deltaproteobacteria and the Firmicutes) have been detected at various locations within the FRC site 97,108,113,[127][128][129][130][131][132][133][134][135][136][137][138][139][140][141] , suggesting that SRMs have successfully adapted to this environment.…”

Dynamics of Microbial Community Composition and Function during In Situ Bioremediation of a Uranium-Contaminated Aquifer

“…All of the these strains have been shown to reduce U(IV) (references 13 and 30 and references therein). Previous studies at the OR-IFRC have suggested that these genera are likely important in U(VI) reduction at this site (5,12). Geobacter spp.…”

“…Experimental sites at the Integrated Field Research Challenge sites at Oak Ridge, TN (OR-IFRC), and Rifle, CO (Rifle-IFRC), have both shown long-term U(VI) reduction (33,38) or sequestration (20). Studies have examined microbial communities during the reduction process, although these have primarily focused on phylogenetic information (5,12,25). However, little research on the functional gene diversity of microbial communities has been reported.…”

From Structure to Function: the Ecology of Host-Associated Microbial Communities

“…to partition the total variance in community structure across sites into the respective contribution of each site property and their covariations. This approach is very popular among general ecologists, with over 1,500 published uses (256), and it is starting to be used by microbial ecologists as well (148,162,169,183,268). Two methods have traditionally been used to partition the variation of community composition data: canonical partitioning and distance partitioning (187,268).…”