![]() For the bioactive wells, the abundance of the U(VI)-reducing generaGeothrix,Desulfovibrio,Ferribacterium, andGeobacterdecreased significantly, whereas the denitrifyingAcidovoraxabundance increased significantly after groundwater invasion. The top 20 major genera accounted for >70% of the cumulative contribution to the dissimilarity in the bacterial communities before and after the groundwater invasion.Castellaniellahad the largest dissimilarity contribution (17.7%). However, both nonmetric multidimensional scaling and analysis of similarity confirmed a significant distinction in the overall composition of the bacterial communities between the bioreduced and the reoxidized sediments. A pairedttest indicated no significant changes of α-diversity for the bioactive wells. To examine the biogeochemical response, high-throughput sequencing and network analysis were applied to characterize bacterial population shifts, as well as cooccurrence and coexclusion patterns among microbial communities. It then was allowed to reoxidize via the invasion of low-pH (3.6 to 4.0), high-nitrate (up to 200 mM) groundwater back into the reduced zone for 1,383 days. The U(VI) was bioreduced to U(IV) and immobilizedin situthrough intermittent injections of ethanol. ABSTRACTA site in Oak Ridge, TN, USA, has sediments that contain >3% iron oxides and is contaminated with uranium (U).
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