Dynamics of Bacterial Communities Mediating the Treatment of an As-Rich Acid Mine Drainage in a Field Pilot.

Elia Laroche,Catherine Joulian,Odile Bruneel,Angélique Desoeuvre,Corinne Casiot,Fabienne Battaglia-Brunet,Marina Héry,Vincent Tardy,Lidia Fernandez-Rojo

doi:10.3389/fmicb.2018.03169

Abstract

Passive treatment based on iron biological oxidation is a promising strategy for Arsenic (As)-rich acid mine drainage (AMD) remediation. In the present study, we characterized by 16S rRNA metabarcoding the bacterial diversity in a field-pilot bioreactor treating extremely As-rich AMD in situ, over a 6 months monitoring period. Inside the bioreactor, the bacterial communities responsible for iron and arsenic removal formed a biofilm (“biogenic precipitate”) whose composition varied in time and space. These communities evolved from a structure at first similar to the one of the feed water used as an inoculum to a structure quite similar to the natural biofilm developing in situ in the AMD. Over the monitoring period, iron-oxidizing bacteria always largely dominated the biogenic precipitate, with distinct populations (Gallionella, Ferrovum, Leptospirillum, Acidithiobacillus, Ferritrophicum), whose relative proportions extensively varied among time and space. A spatial structuring was observed inside the trays (arranged in series) composing the bioreactor. This spatial dynamic could be linked to the variation of the physico-chemistry of the AMD water between the raw water entering and the treated water exiting the pilot. According to redundancy analysis (RDA), the following parameters exerted a control on the bacterial communities potentially involved in the water treatment process: dissolved oxygen, temperature, pH, dissolved sulfates, arsenic and Fe(II) concentrations and redox potential. Appreciable arsenite oxidation occurring in the bioreactor could be linked to the stable presence of two distinct monophylogenetic groups of Thiomonas related bacteria. The ubiquity and the physiological diversity of the bacteria identified, as well as the presence of bacteria of biotechnological relevance, suggested that this treatment system could be applied to the treatment of other AMD.

Highlights

Mining activities produced large amount of wastes composed of sulfide minerals and toxic metallic elements, causing environmental hazard
Biogenic precipitates were collected from tray 1 (T1) and tray 5 (T5) for all the campaigns and from tray 1, 2, 3, 4, and 5 for the D48 and D171 campaigns
The biogenic precipitates that developed inside the pilot contained at least one order of magnitude higher bacterial biomass than what was observed in a lab-scale pilot treating the same acid mine drainage (AMD) (Fernandez-Rojo et al, 2017) and in terraced iron formations reported elsewhere (Brown et al, 2011; Brantner et al, 2014)

Summary

Introduction

Mining activities produced large amount of wastes composed of sulfide minerals and toxic metallic elements, causing environmental hazard. The capacity of autochthonous bacteria to oxidize As(III) into As(V) together with the activity of iron-oxidizing bacteria (FeOB) contribute to the mitigation of the arsenic pollution This natural attenuation has been described at various mining sites worldwide (Casiot et al, 2003; Asta et al, 2010; Egal et al, 2010; Chen and Jiang, 2012; Paikaray, 2015), as well as the diversity of AMD autochthonous microbial communities (Baker and Banfield, 2003; Bruneel et al, 2011; Volant et al, 2014; Méndez-García et al, 2015; Chen et al, 2016). Numerous evidences of the role of the As(III)-oxidizing Thiomonas spp. were reported (Bruneel et al, 2003, 2011; Casiot et al, 2003; Hovasse et al, 2016)

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