Alejandra Giaveno

Biological ferrous sulfate oxidation by A. ferrooxidans immobilized on chitosan beads.

The immobilization of Acidithiobacillus ferrooxidans cells on chitosan and cross-linked chitosan beads and the biooxidation of ferrous iron to ferric iron in a packed-bed bioreactor were studied. The biofilm formation was carried out by using a glass column reactor loaded with chitosan or cross-linked chitosan beads and 9 K medium previously inoculated with A. ferrooxidans cells. The immobilization cycles on the carrier matrix with the bioreactor operating in batch mode were compared. Then, the reactor was operated using a continuous flow of 9 K medium at different dilution rates. The results indicate that the packed-bed reactor allowed increasing the flow rate of medium approximately two fold (chitosan) and eight fold (chitosan cross-linked) without cells washout, compared to a free cell suspension reactor used as control, and to reach ferric iron productivities as high as 1100 and 1500 mg l(-1) h(-1) respectively. Scanning electron microscopy micrographs of the beads, infrared spectroscopy and the X-ray diffraction patterns of precipitates on the chitosan beads were also investigated.

Acidophilic Microorganisms from Geothermal Copahue Volcano System. Assessment of Biotechnological Applications

This work presents an overview of the physicochemical and biological studies carried out along Rio Agrio and in different hot springs belonging to the geothermal Copahue volcano system, in Neuquén Argentina. This is an extreme environment characterized by wide ranges of temperature, pH (<1 to 8) and heavy metals concentration. In these extreme conditions chemolitho-autotrophic bacteria, archaea, heterotrophic bacteria, yeasts and filamentous fungi were detected. Members of Leptospirillum ferrooxidans, Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidianus spp., among others, were successfully cultivated and physiological properties of different isolates were determined. Additionally, bioleaching and biooxidation of regional ores were carried out using mixed native cultures.

Airlift Reactors: Characterization And ApplicationsIn Biohydrometallurgy

Over the last decade biooxidation for the pretreatment of refractory sulfidic gold concentrates and the bioleaching of copper have been applied with increasing frequency. In addition to heap-leach facilities for the bioleaching of copper, several biotank oxidation plants are also operational for the pretreatment stage in the processing of refractory gold ores in large-scale operations (Brierley, 1997; Acevedo, 2000; Rossi, 2001). The application of commercial biooxidation plants using bioreactors started in South Africa and expanded first into Africa and then Australia, South America and, more recently, into China (Morin et al., 2005). These commercial operations show that bioleaching/biooxidation processes can be viable options for the mining industry. Moreover, there is currently a great deal of interest in improving tank technologies for use in the recovery of other metals, such as Cu, Ni, Zn and Co (Brierley & Brierley, 1999; Okibe et al., 2003; Morin et al., 2005; Acevedo & Gentina, 2005; Sand & Gehrke, 2006). The reactors most commonly employed in biohydrometallurgy are the Stirred Tank Reactor (STR), the Bubble Column (BCR) and the Airlift Reactor (ALR). Additionally, cylindrical vessels with a conical bottom known as Pachuca tanks have traditionally been used in biomining. Furthermore, new reactor designs have recently been developed: the Low Energy Bioreactor, the Delft Inclined Plate Bioreactor and the Revolving Drum Bioreactor (Biorotor) (Rossi, 2001). Numerous different papers have been published on bioleaching-biooxidation processes using ALRs and Pachuca tanks (Atkins et al., 1986; Acevedo et al., 1987; Roy et al., 2000; Acevedo, 2000; Rossi, 2001; Mousavi et al., 2005; Shi & Fang, 2005); however, there is limited knowledge on the applications and characterization

Molecular and Morphological Characterization of Cultures from the Extreme Environmental Area of Copahue Volcano-Argentina

This report describes the detection and identification of archaea in several sites located in the area of Copahue volcano, Neuquén province, Argentina by mean of different molecular techniques (PCR, DGGE, DNA sequencing and FISH). In order to study the archaea morphology, cultures were examined using different microscopic techniques (SEM, TEM, EFM and AFM). The corresponding archaea were identified as close relative or members of the genus Acidianus as well as other uncultured archaea clones showing a 93% of similarity to each others.

Oxidative Capacity of Native Strains from Copahue Geothermal System in the Pretreatment of a Gold Sulfide Ore

In this report we evaluate the oxidative capacity of native microorganisms from Copahue geothermal system applied to a gold concentrate (71.1 g/t) compared to that showed by some culture collection strains. The sulphide ore, in which gold is present as submicroscopic particles contained in a pyrite matrix, came from several reservoirs of polymetallic ores located in Neuquén, Patagonia Argentina. The ore was processed in Andacollo treatment plant for gold concentration. After biooxidation tests, the highest percentages of solubilised iron were reached in the inoculated system (100% mixed native cultures, 47.8% Leptospirillum ferrooxidans ATCC 29047 and 28.5% for Acidithiobacillus ferrooxidans DSM 11477) while in the sterile control it was only 8.8%. The gold recovery was 96.3% and 45.3% for the treated and untreated concentrate respectively.

Bioleaching of a Zinc Sulfide Ore by Thermophilic Consortia Isolated from Copahue Volcano

Bioleaching of a sulfide ore was investigated using a consortium of thermophilic bacteria and archaea. The consortium was obtained through successive enrichment procedures (using M88 with tetrathionate) after isolating from two different places into the geothermal area (Baño 9 and Las Maquinitas) of the Copahue volcano (in the north of Neuquén province in Argentina). Bioleaching experiments were carried out in 250-ml shake flasks with 100 ml of media and 1 g of the sulfide ore. Flasks were incubated at 150 rpm and 70 oC. The major constituents of the ore (La Resbalosa, Argentina) were sphalerite, pyrite, chalcopyrite and galena. The sample used throughout bioleaching experiments contained 22.5 % Zn. Two different media (0K and M88) were evaluated with and without the addition of elemental sulfur. Genetic diversity analysis of the microbial community was performed by PCR amplification of bacterial 16S rDNA fragments and analyzed by DGGE (denaturing gradient gel electrophoresis). The 16S rDNA was amplified by using eubacteria and archaea primers. Metal concentration, Eh and pH were periodically analyzed. Solid residues were filtered, washed, dried and finally analyzed by XRD and XRF. After 45 days, more than 50 % of zinc and about 100 % of the copper were solubilized. Galena and jarosite were detected in the solid residues. The data indicated that the dominant acidophiles were bacteria or archaea according to the media. M88 media allowed an important decrease of pH and higher zinc extractions while the presence of sulfur did not show significant influence on the zinc recovery.

Metagenome-Derived Draft Genome Sequence of Acidithiobacillus ferrooxidans RV1 from an Abandoned Gold Tailing in Neuquén, Argentina

In this work we report the metagenome-derived draft genomic sequence of an enrichment culture dominated by A. ferrooxidans obtained from an airlift bioreactor inoculated with the microbial consortium recovered from the “Relave Viejo” tailing. The genome of this culture was assembled de-novo and by reference, generating a consensus assembly of 3.0 Mb. On the basis of 16S rRNA (100 % identity), average nucleotide identity analysis (99.33% identity) and in silico DNA-DNA hybridization against A. ferrooxidans ATCC 23270T (97.9%), the recovered genome is confirmed to pertain to A. ferrooxidans species. Comparative genomics results are presented to uncover the genetic traits of the variant surviving lime treatment and to further explore the genomic diversity of these model iron oxidizing species.

Extremophilic Patagonian Microorganisms Working in Biomining

The microorganisms known as extremophiles have become a powerful tool in the field of biotechnology. Among them, acidophilic and thermophilic microorganisms capable of oxidizing iron(II) or sulfur compounds are very important in ore-processing operations as they are able to enhance the dissolution of sulfide ores. The aim of this chapter is to describe the physiological and phylogenetic characteristics of the main acidophilic species and communities found in geothermal and mining environments in Neuquen Province, Patagonia Argentina, and the advances done by our research group in their application to biomining and bioremediation of heavy metals. Additionally, the chapter includes the description of a novel thermoacidophilic archaeon from the genus Acidianus (Acidianus copahuensis) autochthonous of the Copahue geothermal area isolated and characterized by our research group.

Assessment of Microbial Patagonian Communities for Using in Heavy Metal Bioremediation

Assessing microbial communities in extreme environments allows the search for novel extremophilic microorganisms that can be of use in the development or improvement of biotechnological processes. Most microbial communities developed in such harsh environments have different heavy metal resistance strategies of importance in some technological applications as biomining but also in the bioremediation of metal-polluted environments. In this chapter we describe the microbial diversity of an acidic, volcanic geothermal environment in Northern Patagonia of Argentina: the Copahue geothermal system, containing different geothermal manifestations with temperatures up to 90 °C and pH values from 2 to 7 under aerobic and anaerobic conditions, provoking an enormous biodiversity. In addition, we report some heavy metal applications of those communities, focusing mainly in the bioprecipitation of heavy metals using sulfate-reducing microorganisms.

A Novel Acidianus Strain Isolated from Copahue, Argentina Involved in the Sulphur Cycle of a Volcanic Environment

The extremely thermophilic archaea have become a research hotspot in the recent years because of their extreme living conditions, physicochemical characteristics such as the oxidation of sulphur, metal sulphide ore and excellent leaching capability of metal sulphides. A novel thermoacidophilic archaea (ALE1 strain) of the genus Acidianus, CandidatusAcidianus copahuensis, was isolated from the Copahue Volcano area, in Neuquén, Argentina. This strain was able to metabolize different sulphur compounds under aerobic and anaerobic conditions. ALE1 strain was inoculated in M88, a selective medium for thermoacidophilic archaea recommended by DSMZ. Elemental sulphur (So) and potassium tetrathionate (T) were used alternatively as the energy source, while oxygen and iron (III) were the electron acceptors in the aerobic and anaerobic tests respectively. All systems were incubated at 70oC in shake flasks. The pH, Eh, [H+] and cell concentration were measured. The results from the aerobic test confirm that ALE1 strain was able to oxidize (So) and (T) decreasing the pH significantly, reaching the values 1 and 1.5, respectively. A light yellow precipitate was formed only in the inoculated systems in presence of (T). It was characterized by SEM and FTIR techniques showing that only sulphur atoms are bonded together in some way not confirmed yet. In the anaerobic tests, it was found that ALE1 was able to oxidize sulphur and tetrathionate ion transferring electrons to iron (III) acceptor. The Eh decreased in all inoculated systems from nearly 500mV to 300mV approximately. This work shows that ALE1 strain is helping to keep active the sulphur cycle in the Copahue volcanic environment; however the challenge is to elucidate the metabolism involved.