S56: Bacterial population dynamics in groundwater and surrogate sediments during biostimulation for Cr(VI) reduction

Spatial and temporal water and soil samples (n=34) were collected pre-and post-injection from four wells at the Hanford field site during biostimulation for Cr(VI) reduction.  DNA was extracted from each of the samples and the V1V2 region of the SSU rRNA gene was sequenced via multiplex pyrosequencing. Soil sample populations differed from the corresponding groundwater (even at the phyla level) and were more diverse (p=0.001).  While many of the populations were observed in both groundwater and surrogate sediments, the respective matrices appeared to enrich for particular OTUs.  Of 667 total genera, 141 and 69 were unique to groundwater and soil, respectively. Genera observed only in the sediment included Marinomonas while genera observed only in the groundwater included Desulfonauticus, Desulfomicrobium, and Syntrophobacter. Pseudomonas, Acidovorax, Clostridium, and Herbaspirillum were dominant regardless of sample type.   A prevalence of core genera and rare genera were observed across 34 samples while urban and rural genera were less abundant.  Correlation analyses of genera was done for each sample to estimate population networks.   Metal-reducing organisms such as Geobacter, Desulfovibrio, and Geothrix were correlated in soil while possible fermenting bacteria such as Clostridium, Pelotomaculum, and Pelosinus were correlated in groundwater.  For each well, HRC^® injection resulted in increased diversity, but the greatest changes during stimulation occurred in the populations of mid-dominance either between wells or across time.