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Microbial Ecotoxicology

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Front. Microbiol. | doi: 10.3389/fmicb.2018.02053

Towards integrative bacterial monitoring of metolachlor toxicity in groundwater

  • 1UMR7517 Laboratoire d'hydrologie et de géochimie de Strasbourg (LHYGES), France
  • 2UMR6296 Institut de Chimie de Clermont-Ferrand (ICCF), France
  • 3UMR7156 Génétique moléculaire, génomique et microbiologie (GMGM), France
  • 4Bureau de Recherches Géologiques et Minières, France

Common herbicides such as metolachlor (MET), and their transformation products, are frequently detected in groundwater worldwide. Little is known about the response of groundwater bacterial communities to herbicide exposure, and its potential use for ecotoxicological assessment. The response of bacterial communities exposed to different levels of MET from the Ariège alluvial aquifer (Southwest of France) was investigated in situ and in laboratory experiments. Variations in both chemistry and bacterial communities were observed in groundwater, but T-RFLP failed to uncover a pesticide-specific effect on endogenous bacterial communities. To circumvent issues of hydrogeochemical and seasonal variations in situ, groundwater samples from two monitoring wells of the Ariège aquifer with contrasting records of pesticide contamination were exposed to different levels of MET in laboratory experiments. The standard Microtox® acute toxicity assay did not indicate toxic effects of MET, even at 5 mg L-1 (i.e., 1000-fold higher than in contaminated groundwater). Analysis of MET transformation products and compound-specific isotope analysis (CSIA) in laboratory experiments demonstrated MET biodegradation but did not correlate with MET exposure. High-throughput sequencing analysis (Illumina Miseq) of bacterial communities based on amplicons of the 16S rRNA gene revealed that bacterial community differed mainly by groundwater origin rather than by its response to MET exposure. OTUs correlating with MET addition ranged between 0.4 to 3.6% of the total. Predictive analysis of bacterial functions impacted by pesticides using PICRUSt suggested only minor changes in bacterial functions with increasing MET exposure. Taken together, results highlight MET biodegradation in groundwater, and the potential use of bacterial communities as sensitive indicators of herbicide contamination in aquifers. Although detected effects of MET on groundwater bacterial communities were modest, this study illustrates the potential of integrating DNA- and isotopic analysis-based approaches to improve ecotoxicological assessment of pesticide-contaminated aquifers.

Keywords: Groundwater contamination, microbial ecotoxicology, Chloroacetanilides, Biodegradation, Bacterial communities, Compound-specific isotope analysis

Received: 14 Feb 2018; Accepted: 13 Aug 2018.

Edited by:

Fabrice Martin-Laurent, Institut National de la Recherche Agronomique (INRA), France

Reviewed by:

Xianhua Liu, Tianjin University, China
Catarina R. Marques, University of Aveiro, Portugal  

Copyright: © 2018 Imfeld, Besaury, Maucourt, Donadello, Baran and Vuilleumier. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Gwenaël Imfeld, UMR7517 Laboratoire d'hydrologie et de géochimie de Strasbourg (LHYGES), Strasbourg, France, imfeld@unistra.fr