Bacteria-mediated reduction of As(V)-doped lepidocrocite in a flooded soil sample

Abstract

International audienceUnderstanding the processes involved in the control of arsenic (As) dynamics within soils has become a challenging issue for soil and water quality preservation. Interactions between mineralogical phases, organic ligands and bacterial communities - closely linked to the chemical conditions of the medium - were thus investigated through a geochemical and microbiological experimental study involving the reduction of As(V)-doped lepidocrocite within the soil. Reducing conditions were established as soon as the experiment started, followed by a release of dissolved organic carbon corresponding to a release of acetate. Scanning Electron Microscopy observations pointed out a large bacterial colonization occurring on the lepidocrocite leading to a 3-dimensionally shaped biodissolution of lepidocrocite. The taxonomic diversity evolved throughout the experiment, and thus it demonstrated the evolution of the metabolic activities of the bacteria. At the beginning, lepidocrocite was mainly colonized by bacteria belonging to the Geobacter genus (Deltaproteobacteria) (26%) and Bacillus and Oxalophagus fermentative related genera (Firmicutes) (72%). After two weeks, Geobacter spp. and Firmicutes represented 54% and 30% of the bacterial community, respectively. Although still dominated by Geobacter spp. (34%) at the end of the experiment, the bacterial diversity had increased. After 3 and 8 weeks of incubation, the presence of the arsB and ACR3(1) genes, encoding transporters involved in As detoxification processes, indicated that this community harbored As-resistant or As-transforming genera able to contribute to the transformation of As(V) into As(III)

Highlighting the wide variability in arsenic speciation in wetlands: A new insight into the control of the behavior of arsenic

“…They receive water from three different sources: i) groundwater discharge, ii) subsurface flow and iii) flow from an adjacent surface-water body (Lewis, 1995). During high water levels subsequent to flooding, anaerobic conditions are established and favor the reductive dissolution of wetland soil Fe(III)-oxyhydroxides and associated elements such as As and OM Dia et al, 2015;3 Grybos et al, 2007;Grybos et al, 2009;Olivié-Lauquet et al, 2001). Following its solubilization, As(V) is reduced to As(III), generally by autochthonous bacteria through detoxification or metabolism processes .…”

Poorly Crystalline Fe (III) Oxide excess can to alter the electrochemical paths of soils in the Brazilian Tropical Savannah.

“…All these Fe bio reduction are controlled by general characteristics of ironoxide occurring in the soil (Lovley, 1991(Lovley, , 2013 and can influence the biogeochemistry dynamic (Thompson et al, 2006). Eh changes can direct the type of microorganisms that develops (Husson, 2013), and means imposes the condition for operation of the system (Grybos et al, 2009), since it has the ability to regulate the electrons transferring in the metabolism of microorganisms (DeAngelis et al, 2010;Husson, 2013;Nevin & Lovley, 2002;Sposito 1989), and consequently their development (Dia et al, 2015). The data confirm that all conditions had a similar behavior, with a metabolic inversion to anaerobic microorganisms.…”

“…However, in a more abrupt form, the samples in the presence of the Fe oxide, the depletion is higher in terms of biomass (Figure 4), suggesting that iron, depending on their specie, may create a selective medium and inhibit the development of groups that are more general and benefiting groups that are more specific. Dia et al (2015) comments for every environmental stress there is a multitude of survival strategies for microbial population to acclimate to the new conditions. The same authors say the redox potential in soil indicates changing availability of electron acceptor, requiring fundamental changes in microbial metabolic lifestyles.…”

“…The microbial oxidation of organic compound, associated with Fe (III) reduction form, can to remove of significant amounts of pollutants and contaminants. This ability can be accelerate in areas of flooding conditions with additions of chelating Fe (III) or humic substances (Lovley, 1997;Dia et al, 2015).…”

Comparison of arsenate reduction and release by three As(V)-reducing bacteria isolated from arsenic-contaminated soil of Inner Mongolia, China

“…Some bacteria could directly reduce As(Ⅴ) adsorbed on iron (hydr)oxides, while others could reduce Fe(III) and cause the dissolution of the iron (oxy)hydroxides that will result in As release (Cerkez et al, 2015;Dia et al, 2015;Ehlert et al, 2014;Vaxevanidou et al, 2015). Different As release mechanisms will lead to disparate As release capacities.…”