Phase Preference by Active, Acetate-Utilizing Bacteria at the Rifle, CO Integrated Field Research Challenge Site

Previous experiments at the Rifle, Colorado Integrated Field Research Challenge (IFRC) site demonstrated that field-scale addition of acetate to groundwater reduced the ambient soluble uranium concentration. In this report, sediment samples collected before and after acetate field addition were used to assess the active microbes via <sup>13</sup>C acetate stable isotope probing on 3 phases [coarse sand, fines (8-approximately 150 μm), groundwater (0.2−8 μm)] over a 24-day time frame. TRFLP results generally indicated a stronger signal in <sup>13</sup>C-DNA in the “fines” fraction compared to the sand and groundwater. Before the field-scale acetate addition, a <i>Geobacter-like</i> group primarily synthesized <sup>13</sup>C-DNA in the groundwater phase, an alpha Proteobacterium primarily grew on the fines/sands, and an <i>Acinetobacter sp.</i> and <i>Decholoromonas-like</i> OTU utilized much of the <sup>13</sup>C acetate in both groundwater and particle-associated phases. At the termination of the field-scale acetate addition, the <i>Geobacter-like</i> species was active on the solid phases rather than the groundwater, while the other bacterial groups had very reduced newly synthesized DNA signal. These findings will help to delineate the acetate utilization patterns of bacteria in the field and can lead to improved methods for stimulating distinct microbial populations <i>in situ</i>.