Ecology and Biogeography of Bacterial Communities Associated with Chloroethene-Contaminated Aquifers

Pierre Rossi,Gwenaël Imfeld,Christof Holliger,Florian Kohler,Noam Shani

doi:10.3389/fmicb.2012.00260

Abstract

Massive usage, along with careless handling, storage, spills, and leakages made chloroethenes (CEs) one of the most abundant classes of groundwater contaminants. Anaerobic organohalide respiring bacteria (OHRB) can couple reductive dechlorination of CEs with energy conservation, a central microbial process in (enhanced) natural attenuation of CE-contaminated aquifers. Spatial variability of OHRB guild members present in contaminated sites has not yet been investigated in detail and it is not known whether the spatial localization of contaminated sites could impact differentially remediation capacities. The goal of this study was to investigate how spatially distant microbial communities responded to the presence of CEs. Bacterial communities associated with five geographically distant European CE-contaminated aquifers were analyzed with terminal restriction fragment length polymorphism. Numerical ecology tools were used to assess the separate and combined effects on the communities of their spatial localization, their local environmental conditions and their contaminant concentrations. Three spatial scales were used for the assessment of the structuration of the communities as a function of geographical distances, namely at the aquifer scale, at medium (50 km) and long (ca. 1000 km) distances between aquifers. As a result, bacterial communities were structured with an almost identical contribution by both the geographical position of the aquifer and local environmental variables, especially electron donors and acceptors. The impact of environmental factors decreased with distance between aquifers, with the concomitant increase in importance of a geographical factor. Contrastingly, CEs contributed at a low extent at the medium scale and became important only when all aquifers were considered together, at a large geographical scale, suggesting that distant communities were structured partially by a common niche specialization in organohalide respiration.

Highlights

Invisible above ground, but apparently constantly replenished, groundwater has long been considered as an inexhaustible resource (UNESCO, 2006)
Abiotic processes might be involved in some of the reductive transformations observed in environmental samples, reports in the 1980s indicated that PCE and TCE were reduced biologically under anaerobic conditions into lower chlorinated ethenes, such as cis-dichloroethene and vinyl chloride (VC) and to the harmless ethene
The five aquifers selected in this study, showing clear active OHR processes, did not derogate from this rule (Aeppli et al, 2010; Imfeld et al, 2011)

Summary

Introduction

But apparently constantly replenished, groundwater has long been considered as an inexhaustible resource (UNESCO, 2006). Abiotic processes might be involved in some of the reductive transformations observed in environmental samples, reports in the 1980s indicated that PCE and TCE were reduced biologically under anaerobic conditions into lower chlorinated ethenes, such as cis-dichloroethene (cDCE) and vinyl chloride (VC) and to the harmless ethene Advances in this field showed that selected microorganisms were able to grow using CEs as respiratory terminal electron acceptors, a process termed “OrganoHalide Respiration”(OHR; El Fantroussi et al, 1998; Hendrickson et al, 2002; Duhamel and Edwards, 2006; Heimann et al, 2010). These guild members, which are known to use other electron acceptors than organohalides, are referred www.frontiersin.org

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Results