Monitoring of the biodegradation of toluene-contaminated sand in columns by SIP measurements, CO2 content and its 13C/12C isotopic signature.

Hydrocarbon contaminated soils represent an environmental issue as it impacts on ecosystems and aquifers. Bioremediation uses the ability of bacteria naturally present in the ground to degrade hydrocarbons. It represents an effective solution to fight the pollution but in situ monitoring before and during soil treatment is difficult and challenging. Indeed, where significant subsurface heterogeneity exists, conventional intrusive groundwater sampling can be insufficient to obtain a robust monitoring as the information they provide is restricted to vertical profiles at discrete locations, with no information between sampling points. In order to obtain wider information, complementary methods can be used like geo-electrical techniques. Induced polarization (IP) seems to be the more promising to study the effects of biodegradation processes. Indeed, laboratory and field experiments have shown an enhancement of real and imaginary parts of electrical conductivity while bacterial treatment is progressing (Abdel Aal et al., 2006 ; Atekwana et Atekwana, 2010). Moreover, microbial activity induced CO2 production and isotopic deviation of carbon (Aggarwal and Hinchee, 1991). The ratio δ13C(CO2) will come closer to δ13C(hydrocarbon). From these findings, the French project BIOPHY, supported by the French National Research Agency (ANR), proposes to use electrical methods and gas analyses to develop a non-destructive method for monitoring in situ biodegradation of hydrocarbons in order to optimize soil treatment. Laboratory experiments in columns are carried out to demonstrate its feasibility. Our objectives were to monitor aerobic microbial activity in toluene-contaminated sand columns using complex electrical resistivity measurements (SIP, Spectral Induced polarization and GEIS, Galvanostatic Electrochemical Impedance Spectroscopy) and measuring concentration and δ13C isotopic ratio of produced CO2

Amperometric cytochrome c3-based biosensor for chromate determination

International audienceThe chromate reductase activity of cytochrome c3 (Cyt c3, Mr 13 000), isolated from the sulfate-reducing bacterium Desulfomicrobium norvegicum, was used to develop an amperometric biosensor to measure chromate (CrO42−) bioavailability. The performance of various biosensor configurations for qualitative and quantitative determination of Cr(VI) was studied. Biosensor properties depend on the technique used to immobilize the enzyme on the electrode (glassy carbon electrode). Immobilization of Cyt c3 by entrapment in poly 3,4-ethylenedioxythiophene films denatured the enzyme, while application of an adsorption technique did not affect enzyme activity but the detection range was limited. The best results were obtained with dialysis membranes, which allowed the determination of Cr(VI) from 0.20 to 6.84 mg l−1 (3.85–132 μM) with a sensitivity of 35 nA mg−1 l (1.82 nA μM−1). No interference was observed with As(V), As(III) and Fe(III). Only a small amount of Cyt c3 (372 ng of protein) was needed for this biosensor

Development of an enzymatic amperometric biosensor using cytochromes C3 for the fast quantification of chromate bio-availability in the environment.

International audienceThe presence of toxic Heavy Metals and Metalloids (HMM) in the environment greatly affects the quality of water, soil and chain-food. The toxicity of the HMM depends on metal availability. Many analytical methods, such as sequential extraction or mathematical modelling, have been used for a long time for the assessment of HMM bioavailability. However, these techniques are very often difficult, expensive and long. The biosensors, like analytical tools, have advantages while bringing in addition to specificity, fast and quantitative measurement of a metal that reacts with the biomaterial. This principle is applied to detect the presence of bio-available concentrations of certain metals. The biosensor presented in this study is an amperometric one and its sensitive part is a hemo-protein, the cytochrome c3 from Desulfomicrobium norvegicum. The cytochrome c3 has been chosen for its better properties as a reducing agent of chromate (CrO42-). This study required instrumental developments or adaptations: the development of glassy carbon electrode with immobilized cytochrome c3 and the implementation of electrochemical methods for the study of redox systems, i.e. cyclic voltammetry (CV) and chronoamperometry (CA). The performances of various configurations of biosensors, according to the mode of immobilization of the enzyme, are studied for the qualitative and quantitative determination of chromate. These tools made it possible to identify and follow the redox reactions taking place during the contact of the electrode without and with chromate in solution. The tests on the various configurations of electrode allowed us, for the moment, to choose two promising configurations: The first one is an immobilization of the enzyme with a dialysis membrane and the second is an immobilization with a cellulose nitrate filter. Chromate concentrations from 0.2 to 6.8 mg/L can be detected by the biosensors that were designed

Characterization and mobility of arsenic and heavy metalsinsoils polluted by the destruction of arsenic-containingshells from the Great War

International audienceDestruction of chemical munitions from World War I has caused extensive local top soil contamination by arsenic and heavy metals. The biogeochemical behavior of toxic elements is poorly documented in this type of environment. Four soils were sampled presenting different levels of contamination. The range of As concentrations in the samples was 1937–72,820 mg/kg. Concentrations of Zn, Cu and Pb reached 90,190 mg/kg, 9113 mg/kg and 5777 mg/kg, respectively. The high clay content of the subsoil and large amounts of charcoal from the use of firewood during the burning process constitute an ample reservoir of metals and As-binding materials. However, SEM–EDS observations showed different forms of association for metals and As. In metal-rich grains, several phases were identified: crystalline phases, where arsenate secondary minerals were detected, and an amorphous phase rich in Fe, Zn, Cu, and As. The secondary arsenate minerals, identified by XRD, were adamite and olivenite (zinc and copper arsenates, respectively) and two pharmacosiderites. The amorphous material was the principal carrier of As and metals in the central part of the site. This singular mineral assemblage probably resulted from the heat treatment of arsenic-containing shells. Microbial characterization included total cell counts, respiration, and determination of As(III)-oxidizing activities. Results showed the presence of microorganisms actively contributing to metabolism of carbon and arsenic, even in the most polluted soil, thereby influencing the fate of bioavailable As on the site. However, the mobility of As correlated mainly with the availability of iron sinks

Carbon and arsenic metabolism in Thiomonas strains: differences revealed diverse adaptation processes

<p>Abstract</p> <p>Background</p> <p><it>Thiomonas </it>strains are ubiquitous in arsenic-contaminated environments. Differences between <it>Thiomonas </it>strains in the way they have adapted and respond to arsenic have never been studied in detail. For this purpose, five <it>Thiomonas </it>strains, that are interesting in terms of arsenic metabolism were selected: <it>T. arsenivorans</it>, <it>Thiomonas </it>spp. WJ68 and 3As are able to oxidise As(III), while <it>Thiomonas </it>sp. Ynys1 and <it>T. perometabolis </it>are not. Moreover, <it>T. arsenivorans </it>and 3As present interesting physiological traits, in particular that these strains are able to use As(III) as an electron donor.</p> <p>Results</p> <p>The metabolism of carbon and arsenic was compared in the five <it>Thiomonas </it>strains belonging to two distinct phylogenetic groups. Greater physiological differences were found between these strains than might have been suggested by 16S rRNA/<it>rpoA </it>gene phylogeny, especially regarding arsenic metabolism. Physiologically, <it>T. perometabolis </it>and Ynys1 were unable to oxidise As(III) and were less arsenic-resistant than the other strains. Genetically, they appeared to lack the <it>aox </it>arsenic-oxidising genes and carried only a single <it>ars </it>arsenic resistance operon. <it>Thiomonas arsenivorans </it>belonged to a distinct phylogenetic group and increased its autotrophic metabolism when arsenic concentration increased. Differential proteomic analysis revealed that in <it>T. arsenivorans</it>, the <it>rbc</it>/<it>cbb </it>genes involved in the assimilation of inorganic carbon were induced in the presence of arsenic, whereas these genes were repressed in <it>Thiomonas </it>sp. 3As.</p> <p>Conclusion</p> <p>Taken together, these results show that these closely related bacteria differ substantially in their response to arsenic, amongst other factors, and suggest different relationships between carbon assimilation and arsenic metabolism.</p

Efficacité de biofilms de bactéries As-oxydantes pour l'étape de traitement biologique d'eaux potabilisables arséniées

L'arsenic est un métalloïde toxique dont la présence, relativement fréquente, dans les eaux et les sols est liée soit au fond géochimique, soit aux activités humaines. En ce qui concerne les eaux destinées à la consommation, la législation impose une concentration maximale en arsenic de 10 µg.L-1. Les effets nocifs de l'arsenic sur la santé humaine rendent nécessaire le développement de technologies efficaces et peu couteuse pour éliminer cet élément des eaux potables, ainsi que dans les aquifères pollués et dans les effluents miniers (Wang et Zhao, 2009). Une unité de traitement biologique d'eaux potabilisable faiblement arséniée (As< 50µg/L), couplée à une unité de piégeage de l'As en sortie du bioréacteur, a été mise en œuvre sur un site réel afin d'étudier la robustesse du bioprocédé. Un bioréacteur contenant de la pouzzolane (matériau utilisé dans les traitements d'eaux) a été préalablement ensemencé par une souche bactérienne As(III) oxydante autotrophe (Thiomonas arsenivorans) (Battaglia-Brunet et al., 2002, Michon et al., 2010 ; Wan et al., 2010) puis alimenté par l'eau issue du forage à température ambiante (15-17°C) avec un fonctionnement discontinu (asservissement de l'alimentation du bioréacteur à la pompe du forage d'alimentation en eau). Le suivi du développement du biofilm As(III) oxydant au cours du traitement biologique a été réalisé par la recherche des gènes codant pour l'ARNr 16S (diversité bactérienne totale) et ceux codant pour une arsénite oxydase (aoxB) (diversité des bactéries As(III)-oxydantes). Ce suivi a montré une colonisation rapide et stable du support minéral par des bactéries endogènes de l'eau à traiter. Le rendement d'oxydation de l'étape d'oxydation biologique est compris entre 54 et 100 % avec des temps de séjour de 30 minutes à 7 minutes qui sont comparables à des temps de séjour de techniques classiques de traitement. Les concentrations résiduelles en As en sortie du procédé complet (oxydation biologique + piégeage) sont inférieures à 1 µg/L, et qui sont donc très encourageants pour une application industrielle

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

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

Evaluation of antimony availability in a mining context: Impact for the environment, and for mineral exploration and exploitation.

This work aims to establish Sb mobility, its transfer to biota and its effect on soil health in a semi-arid climate. The results show the presence of stibnite (Sb2S3) as the main primary Sb compound, bindhemite (Pb2Sb2O6(O,OH)), and minor proportions of stibiconite (Sb3+(Sb5+)2O6(OH)) as oxidised Sb species. This research also observes very high total Sb contents in mining materials (max: 20,000 mg kg−1) and soils (400–3000 mg kg−1), with physical dispersion around mining materials restricted to 450 m. The soil-to-plant transfer is very low, (bioaccumulation factor: 0.0002–0.1520). Most Sb remains in a residual fraction (99.9%), a very low fraction is bound to Fe and Mn oxy-hydroxides or organic matter, and a negligible proportion of Sb is leachable. The higher Sb mobility rates has been found under oxidising conditions with a long contact time between solids and water. The main factors that explain the poor Sb mobility and dispersion in the mining area are the low annual rainfall rates that slow down the Sb mobilisation process and the scarce formation of oxidised Sb compounds. All these data suggest poor Sb (III) formation and a low toxicological risk in the area associated with past mining activities. The low mobility of Sb suggests advantages for future sustainable mining of such ore deposits in a semi-arid climate and is also indicative of the limitations of geochemical exploration in the search for new Sb deposits

Genome Sequence of Halomonas sp. Strain A3H3, Isolated from Arsenic-Rich Marine Sediments

We report the genome sequence of Halomonas sp. strain A3H3, a bacterium with a high tolerance to arsenite, isolated from multicontaminated sediments of the l'Estaque harbor in Marseille, France. The genome is composed of a 5,489,893-bp chromosome and a 157,085-bp plasmid

Structure, Function, and Evolution of the Thiomonas spp. Genome

Bacteria of the Thiomonas genus are ubiquitous in extreme environments, such as arsenic-rich acid mine drainage (AMD). The genome of one of these strains, Thiomonas sp. 3As, was sequenced, annotated, and examined, revealing specific adaptations allowing this bacterium to survive and grow in its highly toxic environment. In order to explore genomic diversity as well as genetic evolution in Thiomonas spp., a comparative genomic hybridization (CGH) approach was used on eight different strains of the Thiomonas genus, including five strains of the same species. Our results suggest that the Thiomonas genome has evolved through the gain or loss of genomic islands and that this evolution is influenced by the specific environmental conditions in which the strains live