There is increasing interest in harnessing the functional capacities of 
indigenous microbial communities to transform and remediate a wide range of 
environmental contaminants. Information about which community members respond to 
stimulation can guide the interpretation and development of remediation 
approaches. To comprehensively determine community membership and abundance 
patterns among a suite of samples associated with uranium bioremediation 
experiments, we employed a high-density microarray (PhyloChip). Samples were 
unstimulated, naturally reducing, or collected during Fe(III) (early) and 
sulfate reduction (late biostimulation) from an acetate re-amended/amended 
aquifer in Rifle, Colorado, and from laboratory experiments using 
field-collected materials. Deep community sampling with PhyloChip identified 
hundreds-to-thousands of operational taxonomic units (OTUs) present during 
amendment, and revealed close similarity among highly enriched taxa from drill 
core and groundwater well-deployed column sediment. Overall, phylogenetic data 
suggested that stimulated community membership was most affected by a carryover 
effect between annual stimulation events. Nevertheless, OTUs within the Fe(III)- 
and sulfate-reducing lineages, Desulfuromonadales and Desulfobacterales, were 
repeatedly stimulated. Less consistent, co-enriched taxa represented additional 
lineages associated with Fe(III) and sulfate reduction (e.g. Desulfovibrionales; 
Syntrophobacterales; Peptococcaceae) and autotrophic sulfur oxidation 
(Sulfurovum; Campylobacterales). Data implies complex membership among highly 
stimulated taxa and, by inference, biogeochemical responses to acetate, a 
nonfermentable substrate.