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

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

Contribution à l'étude des mécanismes couplés géochimiques et bactériologiques de transfert de la pollution minière sur le site de Carnoulès (Gard)

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

De la connaissance des microorganismes à la bioremédiation du drainage minier acide de Carnoulès

International audienc

Microbiology of Acid Mine Drainage: from natural attenuation to bioremediation.

International audienc

Vers la bioremédiation des eaux acides arséniées ?

International audienc

Le devenir des contaminants métalliques dans l'environnement aquatique sous le contrôle des micro-organismes? Cas des Drainages miniers acides

International audienc

The Carnoules mine. Generation of As-rich acid mine drainage, natural attenuation processes and solutions for passive in-situ remediation

7 pagesThe former Carnoules Pb-Zn mine (Department of Gard, France) has produced 1.5 Mt of solid waste containing pyrite and associated metals and metalloids including arsenic and thallium. The tailings are stored behind a dam. Upon oxidation they generate acid (pH≤3) water containing up to 350mg/l of arsenic, 750 to 2700mg/L of iron, sulphate (2000-7500mg/L) and a few mg/L of heavy metals (Pb, Zn, Cd). The water surges at the bottom of the dam forming the Reigous Creek. For the last ten years, the physicochemical, biological, mineralogical and hydrological characteristics of the site have been monitored by the Hydrosciences laboratory with the aim of understanding the processes responsible for the release of pollutants in the tailing stock and of reducing pollution in the mining creek. The results of this study indicate that, unlike at other sites, pyrite oxidation takes place at the bottom of the tailing stock at the entry of oxygenated underground water. The bacterial populations that are present in the tailings and may catalyse the oxidation reactions were identified. About 20 to 30% of the arsenic initially present in the spring water in the form of As(III), precipitates with Fe in less than 30 meters. This leads to the formation of ochre precipitates containing 20% of arsenic around bacterial structures. Several organisms (bacteria and euglena) that mediate Fe and As oxidation in the creek and thus contribute to accelerating arsenic retention in the solid phase were identified. On the basis of these results and pilot plant experiments, solutions for passive in-situ bioremediation are proposed

The rhizosphere of Sulla spinosissima growing in abandoned mining soils is a reservoir of heavy metals tolerant plant growth-promoting rhizobacteria

International audienceHeavy metals tolerant soil bacteria are known to play essential roles in biogeochemical cycles, biotransformation of metals, bioremediation processes and, plant adaptation. The objective of this study was to isolate and characterize the bacterial strains associated with Sulla spinosissima, a native legume species growing in three abandoned mining sites situated in the Oujda region (East Morocco). Globally, more than 370 bulk and rhizospheric soil bacteria were isolated. Their identification by 16S rDNA sequencing showed that dominant phyla were Firmicutes, Actinobacteria, and Proteobacteria, while at the genus level Bacillus dominated, followed by Stenotrophomonas, Arthrobacter, and Rhodococcus. All the soils contained strains possessing plant growth-promoting traits. The best-performing strains were LMR283 for auxin production (145 μg mL−1), LMR291 for phosphate solubilization (67.6 mg L−1), LMR280 for siderophore production (92.4%) and LMR326 for ACC deaminase activity (105 nmoL α-ketobutyrate mg−1 h−1). Among tolerant PGP bacteria, 17 isolates showed antagonistic activity against the pathogen Fusarium oxysporum and 26 produced lytic enzymes. It was relevant that the rhizospheric soils prospected compared to bulk soils contained more interesting isolates for all the studied properties, in particular for soils sampled from Oued El Heimer and Sidi Boubker sites (respectively 79 and 63% of performing strains). Data presented here indicate that Sulla spinosissima growing in heavy metal soils is associated with multifarious active bacterial populations that probably sustain plant tolerance and growth under the prevailing stressful conditions. Superior strains identified are good candidates to be used with selected plants in rehabilitation programs in the contaminated ecosystems

Characterization of plant growth promoting activities of indigenous bacteria of phosphate mine wastes, a first step toward revegetation

International audienceMorocco holds the vast majority of the world’s phosphate reserves, but due to the processes involved in extracting and commercializing these reserves, large quantities of de-structured, nutritionally deficient mine phosphate wastes are produced each year. In a semi-arid climate, these wastes severely hamper plant growth and development leading to huge unvegetated areas. Soil indigenous Plant Growth-Promoting Bacteria (PGPB) play a pivotal role in restauration of these phosphate mining wastes by revegetation, by increasing plants development, soil functioning, and nutrient cycling. The development of a vegetative cover above the degraded phosphate wastes, could stabilize and reintegrate these wastes in the surrounding environment. The current study’s objectives were to isolate, characterize, and identify indigenous bacterial strains, and test their PGP activity in vitro and, for the best-performing strains in planta , in order to assess their potential for acting as biofertilizers. A quantitative test for the synthesis of auxin and the production of siderophores as well as a qualitative test for the solubilization of phosphate were performed on all isolated bacterial strains. The production of hydrogen cyanide (HCN), exopolysaccharides (EPS), and enzymes were also examined. Three bacteria, selected among the best PGPB of this study, were tested in planta to determine whether such indigenous bacteria could aid plant growth in this de-structured and nutrient-poor mining soil. Using 16S rRNA gene sequencing, 41 bacterial strains were isolated and 11 genera were identified: Acinetobacter, Agrococcus, Bacillus, Brevibacterium, Microbacterium, Neobacillus, Paenibacillus, Peribacillus, Pseudarthrobacter, Stenotrophomonas , and Raoultella . Among the three best performing bacteria (related to Bacillus paramycoides, Brevibacterium anseongense , and Stenotrophomonas rhizophila ), only Stenotrophomonas rhizophila and Brevibacterium anseongense were able to significantly enhance Lupinus albus L. growth. The best inoculation results were obtained using the strain related to Stenotrophomonas rhizophila , improving the plant’s root dry weight and chlorophyll content. This is also, to our knowledge, the first study to show a PGP activity of Brevibacterium anseongense