Impact of iron-bearing minerals on microbial communities in nitrate polluted karst aquifer

Groundwater nitrate pollution is a major reason for deteriorating water quality and thus a potential threat to human and animal health. One approach to eliminate nitrate is based on the activation of the natural bioremediation potential by stimulating the groundwater microbial community in situ. Most groundwater systems are limited in bioavailable organic carbon, thus limiting the potential for efficient nitrate removal by denitrifying organotrophs. To determine the potential for chemolithotrophic pathways four different iron-bearing minerals were incubated in groundwater monitoring wells using self constructed microbial trapping devices (MTDs). Phylogenetic analyses based on 16S rRNA sequences revealed that the iron minerals had an impact on the composition of the locally stimulated microbial community. We demonstrate that our approach is a cost-effective way for investigating and stimulating specific target groups of microorganisms in groundwater. Moreover, our data do not only provide valuable insights in the metabolic flexibility of the karst aquifer microbial community, but also substantiates the metabolic potential for anaerobic Fe(II) oxidation using nitrate as oxidant.