Microbial community dynamics during acetate biostimulation of RDX-contaminated groundwater

Biostimulation of groundwater microbial communities (e.g., with carbon sources) is a common approach to achieving in situ bioremediation of organic pollutants (e.g., explosives). We monitored a field-scale approach to remediate the explosive RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) in an aquifer near the Iowa Army Ammunition Plant in Middletown, IA. The purpose of the study was to gain insight into the effect of biostimulation on the microbial community. Biostimulation with acetate led to the onset of RDX reduction at the site, which was most apparent in monitoring well MW309. Based on previous laboratory experiments, we hypothesized that RDX degradation and metabolite production would correspond to enrichment of one or more Fe(III)-reducing bacterial species. Community DNA from MW309 was analyzed with 454 pyrosequencing and terminal restriction fragment length polymorphism. Production of RDX metabolites corresponded to a microbial community shift from primarily Fe(III)-reducing Betaproteobacteria to a community dominated by Fe(III)-reducing Deltaproteobacteria (Geobacteraceae in particular) and Bacteroidetes taxa. This data provides a firsthand field-scale microbial ecology context to in situ RDX bioremediation using modern sequencing techniques that will inform future biostimulation applications.