Papers by Keyword: Archaea

Abstract: The aim of this study was to investigate the microbial colonization and arsenic leaching kinetics of South Korean mine tailings containing arsenopyrite at fixed temperatures (20°C, 30°C and 45°C) and at ramped up temperatures (25 to 45°C, with a 2°C daily increase). The experiments were conducted in a packed bed of inert granite pebbles coated with the tailings material and leached with a mesophilic culture dominated by Acidithiobacillus caldus (56%), a lesser percentage of Leptospirillum ferriphilum (29%) and Archaea (15%), using 1 g/L ferrous-enriched 0K medium. The ramped-up temperature experiment was conducted in triplicate and columns were sacrificed after different leach periods to study the evolution of microbial species dominating the colonization. The leaching performance was evaluated using the arsenic released into solution, the iron oxidation rates, the pH and the redox potential. The microbial speciation of the culture attached to the solids during the leach experiment was determined upon completion of each experiment. A steady arsenic solubilisation of between 94 and 97% was observed among the various column experiment after 88 days post inoculation. Microbial speciation performed following the leaching of the mineral indicated a shift of microbial communities in the columns when compared to the initial inoculum.

Abstract: Pyrometallurgical copper final slag was subjected to leaching by means microbial cultures of three different groups based on their optimum temperature for growth and activity: mesophilic and moderate thermophilic bacteria, and extreme thermophilic archaea. The leaching experiments were performed by the shake-flask technique and in agitated bioreactors under batch and continuous-flow conditions. The effect of the most essential factors (particle size, pulp density, pH, aeration) on this process was studied. The highest rates of extraction of the non-ferrous metals (Cu, Zn, Co) and iron were achieved by means of some archaea but at relatively low pulp densities (5 – 10%). Some moderate thermophilic bacteria were the most efficient at the higher pulp densities (15 – 20 %). The, leaching by some mesophiles at pH 3.0 – 3.5 was also very attractive since it was connected with high extractions of these metals (about 85 – 92% at 20% pulp density), much lower acid consumption and low solubiliation of fayalite which resulted in the production of pregnant solutions suitable for the recovery of the dissolved non-ferrous metals.

Abstract: This study is the first demonstration of a continuous culture bio-catalysed iron oxidation and jarosite precipitation reactor using thermophilic archea, for use in hydrometallurgical process flow sheets. A two-stage continuous stirred tank reactor (CSTR) system comprised of two CSTRs, each with its own settler, was operated for biological iron oxidation and precipitation at 70°C. The two-stage design was to allow the growth of microorganisms that prefer various redox regimes. The bioreactors were inoculated with a mixed culture of extreme thermophilic iron oxidisers from genera Acidianus, Metallosphaera and Sulfolobus. The influent (pH 1.5) contained (g L^-1) 15 Fe²⁺, 1.5 Cu, 1.5 Ni (all as sulfates), nutrients and trace elements. At a hydraulic retention time (HRT) of 6-7 h in each CSTR, the overall iron oxidation rate was 1.0±0.1 g L^-1 h^-1 and percent 97±2%. The pH values were 1.38±0.16 and 1.57±0.05, and redox potentials (Ag/AgCl reference) were474±47 mV and 575±1 mV, in CSTR1 and CSTR2, respectively. The percentages of influent Fe, Cu and Ni removed as precipitates from settlers were 52%, 0.46% and 0.03%, respectively. The precipitates were comprised of jarosite (100%), potassium jarosite being the dominant form (38-51%), followed by hydronium (30-35%), ammonium (13-18%) and sodium jarosites (6-9%). The precipitates had a sludge volume index of 5.8-19 mL g^-1, indicating good settling properties facilitating easy removal through settling. The simultaneous and instantaneous addition of contaminants (g L^-1: 2.0 Al, 0.05 As, 0.05 F, 0.2 Co, 5.0 Mg and 0.4 Mn), potentially contained in hydrometallurgical processing streams, into the influent decreased the iron oxidation (50% overall oxidation with HRT of 26-29 h in each CSTR) and jarosite content in precipitates (85-87%). In conclusion, the two-stage high-temperature CSTR system allowed iron oxidation and precipitation of the oxidised iron in the form of well settling jarosite with only minor loss of Cu and Ni via co-precipitation. However, the bioreactor performance was hampered by the introduction of other transition metals, fluoride and arsenic.

Abstract: Biofilm formation of microorganisms on relevant surfaces is of great importance for biomining and acid mine drainage (AMD). Thermo-acidophilic archaea like Acidianus, Sulfolobus and Metallosphaera are of special interest due to their ability to enhance leaching rates. Visualization and investigation of microbial attachment and biofilm formation of metal-oxidizing organisms up to now has been done mostly with mesophilic or moderately thermophilic bacteria. In this study, attachment and biofilms by the crenarchaeota Sulfolobus metallicus DSM 6482^T and a new isolate Acidianus sp. DSM 29099 on sulfur or pyrite were analyzed. Confocal laser scanning microscopy (CLSM) combined with fluorescent dyes specific for nucleic acids or glycoconjugates were used to monitor biofilm formation on surfaces. The data indicate that cell attachment and the subsequently formed biofilm structures were species and substrate dependent. The investigation of binary biofilms on pyrite showed that both species were heterogeneously distributed on pyrite surfaces in the form of individual cells or microcolonies. In addition, physical contact between the two species was visible, as revealed by specific lectins able to distinguish single species.

Abstract: Laboratory scale (7 L) reactors, inoculated with the L. ferriphilum dominated BIOX inoculum, were used to test the stability of the community under controlled conditions. Further, the effect of increased temperature, solids loading and pH fluctuations on the bioleaching performance and community structure were studied. Both performance and community structure remained stable under controlled conditions (41.5°C, 20% solids loading, 7 day residence time). Increasing the solids loading to 31% did not significantly affect performance or community structure. An increase in temperature (2°C every 10 days) did not have a significant effect up to 48°C, but the increase from 48°C to 50°C resulted in the loss of L. ferriphilum and a decrease in leaching performance. A more gradual increase (1°C increments) from 48°C to 50°C resulted in a stable community, dominated by Ac. cupricumulans and Acidithiobacillus caldus. A similar shift in community structure was observed when the pH fell below pH 0.8, but this was transient and L. ferriphilum recovered dominance upon adjustment to a pH > 1.0. A further increase in temperature to 52°C resulted in the loss of At. caldus and the emergence of Sulfobacilli. However, leaching performance under these conditions was poor, despite the presence of over 10 g/L ferric iron. In addition, yeast extract was required to maintain high cell numbers at 52°C. This work has identified a selection of conditions under which the community in BIOX reactors could evolve dynamically towards those communities currently observed in commercial operations.

Abstract: In batch cultures, the presence of nitrate inhibited iron (II) oxidation by iron (II)- or tetrathionate-adapted Acidianus (A.) brierleyi and Sulfolobus (S.) metallicus cells and tetrathionate oxidation by iron (II)-adapted A. brierleyi cells. Tetrathionate-adapted cell lines of A. brierleyi and S. metallicus oxidised tetrathionate in the presence of up to 40 mM nitrate but cell numbers were lower than those in uncontaminated tests. The results of the bioleaching tests indicated a possible window of enhanced copper extraction in the presence of 2030 mM nitrate that might be exploited in tank bioleaching. The build up of nitrate above 40 mM in bioleaching solutions must be avoided

Abstract: In this work we have studied the attachment and colonization of pyrite surfaces by the recently isolated thermophilic archaeon Candidatus Acidianus copahuensis (isolated from the geothermal Caviahue-Copahue system, Argentina). Cells pregrown with sulfur, iron (II) or pyrite were tested. In order to characterize the EPS glycoconjugates of this strain, fluorescent lectins were used. Concanavalin A (ConA) gave the best signal and was selected for further studies. Coupons and grains of pyrite were treated with DAPI (to stain attached cells) and TRITC-ConA (to stain polysaccharides from EPS). Pyrite surfaces were imaged by epifluorescence (EFM) and confocal laser microscopy (CLSM). Initial cell attachment to pyrite grains was estimated to be 26%, 35% and 43% when cells were pregrown with sulfur, iron (II) and pyrite as electron donors, respectively. It was observed that the cell adhesion correlated with an increase of EPS production; both processes were favoured when cells were pregrown with pyrite or iron (II). Also the effect of phosphate (Pi) starvation in the attachment of Acidianus was studied in similar tests using a base medium without Pi. An increase of cell attachment under Pi starvation conditions was detectable.

Abstract: Acidic saline lake systems are an uncommon type of natural extreme environment described in Northern Chile and in Australia. These environments are considered a terrestrial analogue to certain ancient Martian terrains and a source of new material for biotechnological applications as bioleaching at high ionic strength conditions and biological systems for precipitating metal sulfides. The aim of this study is to describe the occurrence of redox couples that support prokaryotic life in the system and to obtain representative cultures of predominant microorganisms/metabolisms. Mapping of the area of interest and geochemical analysis of sediments, bedrock and water samples were performed. The original microbial community and enriched cultures were studied by direct count and culturing dependent and independent techniques. In the distal part of the alluvial fans some ponds are found with acidic brines (up to pH 1) of the Cl-SO4-Na (-Mg) type that are surrounded by yellow efflorescences. Other ponds towards the basin center progressively increase in concentration due to capillary evaporation. Brines are rich in aluminium and boron with lower concentration of manganese, lithium, iron and arsenic. An advanced hydrothermal argillic alteration affecting the country rocks, native sulfur associated to active solfataras, alunite and jarosite occurrences in sediments and chloride and sulfate efflorescent salts were evidenced. The microbial community in brines and sediments (10⁵ and 10⁶ cells/mL, respectively) was dominated by Firmicutes, Proteobacteria and Actinobacteria, and by Proteobacteria and Cyanobacteria, respectively. Sulphur and iron oxidation activity were detected depending on the salinity of the samples. Culture enrichments that respire and reduce As (V) and sulfate have been only obtained from sites with the highest pH (4-5). Microbial assemblages in those heterotrophic cultures were closely related to the Gamma and Betaproteobacteria, meanwhile, Rhodanobacter and Shewanella were the only microorganisms detected in the autotrophic cultures supplemented by Na₂S and by H₂. Relevant information to describe the occurring surface biogeochemical processes in that acidic saline system has been obtained. In addition, the occurrence of new prokaryotic genera capable of arsenic redox transformation has been evidenced in acidic systems.

Abstract: Lateritic deposits contain oxide ores and usually consist of three layers, namely the limonitic, the saprolite and the garnieritic layer. Limonite, which comprises the top lateritic layer, is a homogeneous ore consisting mainly of goethite with which nickel is associated. Microbe-mineral interactions are of interest for biogeochemical cycles. Microorganisms which are able to mediate redox transformation of Fe-oxide containing minerals are of particular interest when effective bioremediation strategies for insoluble hydroxide and oxide minerals are designed. Quantitive real-time polymerase chain reaction (qPCR) is a culture independent method which is used for the quantification of environmental microorganisms. The aim of this work was to enumerate the microorganisms in different lateritic deposits at Moa mine (Holguin, Cuba) by qPCR and also to obtain Fe (III)-reducing enrichment cultures. A higher microbial abundance was detected in the sampling sites 5124 and 5125 and a lower one in the site 5121. Both, Archaea and Bacteria occurred in all samples except for site 5121 where Bacteria were not detected by qPCR. The Geobacteraceae which comprise Fe-(III)-reducing bacteria were detected at all five lateritic ore sites. The results indicate that these bacteria play a role fundamental in the formation of sediments with a number of oxidized or partially oxidized iron compounds such as magnetite, hematite, goethite and various Fe (III)-oxyhydroxides.

Abstract: Biofilm development of F. acidiphilum BRGM4 on polycarbonate filters floating on liquid medium and pyrite surfaces were studied by confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) combined with epifluorescence microscopy (EFM). Results show that F. acidiphilum biofilms were heterogeneously distributed, and varied among different growth conditions, such as inorganic phosphate (P_i) starvation and glucose supplementation. Biofilm and planktonic cells showed significant morphological differences. Capsular EPS were observed in both biofilm and planktonic cells. Cells showed preferential attachment to the cracks/defects of pyrite surfaces.