Characterization of Groundwater Microbial Communities, Dechlorinating Bacteria, and In Situ Biodegradation of Chloroethenes Along a Vertical Gradient

Abstract

The variability of hydrogeochemical conditions can affect groundwater microbial communities and the natural attenuation of organic chemicals in contaminated aquifers. It is suspected that in situ biodegradation in anoxic plumes of chloroethenes depends on the spatial location of the contaminants and the electron donors and acceptors, as well as the patchiness of bacterial populations capable of reductive dechlorination. However, knowledge about the spatial variability of bacterial communities and in situ biodegradation of chloroethenes in aquifers is limited. Here, we show that changes of the bacterial communities, the distribution of putative dechlorinating bacteria and in situ biodegradation at the border of a chloroethenes plume (Bitterfeld, Germany) are related to local hydrogeochemical conditions. Biotic reductive dechlorination occurred along a 50 m vertical gradient, although significant changes of the hydrogeochemistry and contaminant concentrations, bacterial communities and distribution of putative dechlorinating bacteria (Dehalobacter spp., Desulfitobacterium spp., Dehalococcoides spp., and Geobacter spp.) were observed. The occurrence and variability of in situ biodegradation of chloroethenes were revealed by shifts in the isotope compositions of the chloroethenes along the vertical gradient (δ 13 C ranging from −14.4‰ to −4.4‰). Our results indicate that habitat characteristics were compartmentalized along the vertical gradient and in situ biodegradation occurred with specific reaction conditions at discrete depth. The polyphasic approach that combined geochemical and biomolecular methods with compound-specific analysis enabled to characterize the spatial variability of hydrochemistry, bacterial communities and in situ biodegradation of chloroethenes in a heterogeneous aquifer.

Validation of an Integrative Methodology to Assess and Monitor Reductive Dechlorination of Chlorinated Ethenes in Contaminated Aquifers

“…Based on our expertise in the field of reductive dechlorination (e.g., Holliger et al, 1993;Holliger and Schumacher, 1994;Holliger et al, 1997;Imfeld et al, 2011;Rossi et al, 2012), numerical ecology as well as bacterial community analyses (e.g., Fromin et al, 2002;Jossi et al, 2006;Rossi et al, 2009Rossi et al, , 2012, a comprehensive methodology for the assessment of the in situ potential for complete reductive dechlorination in contaminated aquifers was established (Tarnawski et al, 2015). The methodology adopts an ecological approach (de Lorenzo, 2008;Chakraborty et al, 2012) and examines simultaneously geochemical and microbiological data sets to assess the aquifer functioning and the fate of the contaminants.…”

Multiple Factor Analysis for Contingency Tables in the FactoMineR Package

“…• The relationship between the bacterial community structures and hydrogeochemical conditions in a groundwater study (Imfeld et al, 2011).…”

Rapid Enrichment of Dehalococcoides-Like Bacteria by Partial Hydrophobic Separation

“…and a broader group of the Chloroflexi, including organisms found in uncontaminated environments (18). The organisms targeted by these primers are almost certainly not all organohalide-respiring bacteria but contain known organohalide-respiring bacteria and target phylogenetically related unknown and less-studied bacteria that may in fact be organohalide respiring (35,36). The total number of 16S rRNA genes was quantified with general bacterial primers targeting the V3 region of the 16S rRNA gene (37).…”