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  • 1. Bramble, J L
    et al.
    Graves, D J
    Brodelius, Peter
    Department of Plant Biotechnology, University of Lund.
    Calcium and Phosphate Effects on Growth and Alkaloid Production in Coffea arabica: Experimental Results and Mathematical Model.1991In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 37, no 9, p. 859-868Article in journal (Refereed)
    Abstract [en]

    Plant, mammalian, and microbial cells are commonly immobilized in calcium alginate gels for the production of valuable secondary metabolites. However, calcium ions are known to inhibit growth in various type of cells, and calcium is an integral part of such gels. Therefore, an investigation was conducted to evaluate the effect of calcium on the growth and alkaloid production of a model cell-line, Coffea arabica, in suspension culture before attempting to immobilize such cells in alginate. A kinetic model was then developed from the results to describe cell growth and alkaloid production and the mechanism by which calcium influences these variables. In addition, it was observed that there was a characteristic relationship between the concentration of calcium in the external medium and the concentration of extracellular and intracellular phosphate. The intracellular phosphate level was, in turn, related to the production of alkaloids. Using these results, a dynamic mathematical model of cell growth and alkaloid production was developed based on the proposed roles of calcium and phosphate. The model showed satisfactory agreement with three sets of experiments at different calcium concentrations. A possible linkage between the calcium and phosphate results is postulated based on the limited solubility of calcium phosphate. 

  • 2.
    Dopson, Mark
    et al.
    Umeå University.
    Halinen, A.-K.
    Tampere Univ Technol, Finland.
    Rahunen, N.
    Tampere Univ Technol, Finland.
    Boström, Dan
    Umeå University.
    Sundkvist, J.-E.
    Boliden Mineral AB, Boliden, Sweden.
    Riekkola-Vanhanen, M.
    Talvivaara Project Ltd, Sotkamo, Finland.
    Kaksonen, A.H.
    Tampere Univ Technol, Finland.
    Puhakka, J. A.
    Tampere Univ Technol, Finland.
    Silicate mineral dissolution during heap bioleaching2008In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 99, no 4, p. 811-820Article in journal (Refereed)
    Abstract [en]

    Silicate minerals are present in association with metal sulfides in ores and their dissolution occurs when the sulfide minerals are bioleached in heaps for metal recovery. It has previously been suggested that silicate mineral dissolution can affect mineral bioleaching by acid consumption, release of trace elements, and increasing the viscosity of the teach solution. In this study, the effect of silicates present in three separate samples in conjunction with chalcopyrite and a complex multi-metal sulfide ore on heap bioleaching was evaluated in column bioreactors. Fe2+ oxidation was inhibited in columns containing chalcopyrite samples A and C that leached 1.79 and 1.11 mM fluoride, respectively but not in sample B that contained 0.14 mM fluoride. Microbial Fe2+ oxidation inhibition experiments containing elevated fluoride concentrations and measurements of fluoride release from the chalcopyrite ores supported that inhibition of Fe2+ oxidation during column leaching of two of the chalcopyrite ores was due to fluoride toxicity. Column bioleaching of the complex sulfide ore was carried out at various temperatures (7-50 degrees C) and pH values (1.5-3.0). Column leaching at pH 1.5 and 2.0 resulted in increased acid consumption rates and silicate dissolutionsuch that it became difficult to filter the leach solutions and for the leach liquor to percolate through the column. However, column temperature (at pH 2.5) only had a minor effect on the acid consumption and silicate dissolution rates. This study demonstrates the potential negative impact of silicate mineral dissolution on heap bioleaching by microbial inhibition and liquid flow.

  • 3.
    Dopson, Mark
    et al.
    Umeå University.
    Halinen, Anna-Kaisa
    Tampere University of Technology, Tampere, Finland.
    Rahunen, Nelli
    Tampere University of Technology, Tampere, Finland.
    Özkaya, Bestamin
    Tampere University of Technology, Tampere, Finland.
    Sahinkaya, Erkan
    Tampere University of Technology, Tampere, Finland.
    Kaksonen, Anna H
    Tampere University of Technology, Tampere, Finland.
    Lindström, E Börje
    Umeå University.
    Puhakka, Jaakko A
    Tampere University of Technology, Tampere, Finland.
    Mineral and iron oxidation at low temperatures by pure and mixed cultures of acidophilic microorganisms.2007In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 97, no 5, p. 1205-1215Article in journal (Refereed)
    Abstract [en]

    An enrichment culture from a boreal sulfide mine environment containing a low-grade polymetallic ore was tested in column bioreactors for simulation of low temperature heap leaching. PCR-denaturing gradient gel electrophoresis and 16S rRNA gene sequencing revealed the enrichment culture contained an Acidithiobacillus ferrooxidans strain with high 16S rRNA gene similarity to the psychrotolerant strain SS3 and a mesophilic Leptospirillum ferrooxidans strain. As the mixed culture contained a strain that was within a clade with SS3, we used the SS3 pure culture to compare leaching rates with the At. ferrooxidans type strain in stirred tank reactors for mineral sulfide dissolution at various temperatures. The psychrotolerant strain SS3 catalyzed pyrite, pyrite/arsenopyrite, and chalcopyrite concentrate leaching. The rates were lower at 5 degrees C than at 30 degrees C, despite that all the available iron was in the oxidized form in the presence of At. ferrooxidans SS3. This suggests that although efficient At. ferrooxidans SS3 mediated biological oxidation of ferrous iron occurred, chemical oxidation of the sulfide minerals by ferric iron was rate limiting. In the column reactors, the leaching rates were much less affected by low temperatures than in the stirred tank reactors. A factor for the relatively high rates of mineral oxidation at 7 degrees C is that ferric iron remained in the soluble phase whereas, at 21 degrees C the ferric iron precipitated. Temperature gradient analysis of ferrous iron oxidation by this enrichment culture demonstrated two temperature optima for ferrous iron oxidation and that the mixed culture was capable of ferrous iron oxidation at 5 degrees C.

  • 4.
    Gahan, Chandra Sekhar
    et al.
    Luleå University of Technology.
    Sundkvist, Jan-Eric
    Luleå University of Technology ; Boliden Mineral AB, Boliden, Sweden.
    Dopson, Mark
    Umeå University.
    Sandström, Åke
    Luleå University of Technology.
    Effect of chloride on ferrous iron oxidation by a Leptospirillum ferriphilum-dominated chemostat culture2010In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 106, no 3, p. 422-431Article in journal (Refereed)
    Abstract [en]

    Biomining is the use of microorganisms to catalyze metal extraction from sulfide ores. However, the available water in some biomining environments has high chloride concentrations and therefore, chloride toxicity to ferrous oxidizing microorganisms has been investigated. Batch biooxidation of Fe(2+) by a Leptospirillum ferriphilum dominated culture was completely inhibited by 12gL(-1) chloride. In addition, the effects of chloride on oxidation kinetics in a Fe(2+) limited chemostat were studied. Results from the chemostat modeling suggest that the chloride toxicity was attributed to affects on the Fe2+ oxidation system, pH homeostasis, and lowering of the proton motive force. Modeling showed a decrease in the maximum specific growth rate (mu(max)) and an increase in the substrate constant (K(s)) with increasing chloride concentrations, indicating an effect on the Fe(2+) oxidation system. The model proposes a lowered maintenance activity when the media was fed with 2-3 g L(-1) chloride with a concomitant drastic decrease in the true yield (Y(true)). This model helps to understand the influence of chloride on Fe(2+) biooxidation kinetics.

  • 5.
    Kupka, Daniel
    et al.
    Slovak Academy of Sciences, Košice, Slovakia.
    Rzhepishevska, Olena I.
    Umeå University.
    Dopson, Mark
    Umeå University.
    Lindström, E. Börje
    Umeå University.
    Karnachuk, Olia V.
    Tomsk State University, Tomsk, Russia.
    Tuovinen, Olli H.
    Ohio State University, USA.
    Bacterial oxidation of ferrous iron at low temperatures2007In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 97, no 6, p. 1470-1478Article in journal (Refereed)
    Abstract [en]

    This study comprises the first report of ferrous iron oxidation by psychrotolerant, acidophilic iron-oxidizing bacteria capable of growing at 5 degrees C. Samples of mine drainage-impacted surface soils and sediments from the Norilsk mining region (Taimyr, Siberia) and Kristineberg (Skellefte district, Sweden) were inoculated into acidic ferrous sulfate media and incubated at 5 degrees C. Iron oxidation was preceded by an approximately 3-month lag period that was reduced in subsequent cultures. Three enrichment cultures were chosen for further work and one culture designated as isolate SS3 was purified by colony isolation from a Norilsk enrichment culture for determining the kinetics of iron oxidation. The 16S rRNA based phylogeny of SS3 and two other psychrotolerant cultures, SS5 from Norilsk and SK5 from Northern Sweden, was determined. Comparative analysis of amplified 16S rRNA gene sequences showed that the psychrotolerant cultures aligned within Acidithiobacillus ferrooxidans. The rate constant of iron oxidation by growing cultures of SS3 was in the range of 0.0162-0.0104 h(-1) depending on the initial pH. The oxidation kinetics followed an exponential pattern, consistent with a first order rate expression. Parallel iron oxidation by a mesophilic reference culture of Acidithiobacillus ferrooxidans was extremely slow and linear. Precipitates harvested from the 5 degrees C culture were identified by X-ray diffraction as mixtures of schwertmannite (ideal formula Fe(8)O(8)(OH)(6)SO(4)) and jarosite (KFe(3)(SO(4))(2)(OH)(6)). Jarosite was much more dominant in precipitates produced at 30 degrees C. Biotechnol. Bioeng. 2007;97:1470-1478. (c) 2007 Wiley Periodicals, Inc.

  • 6.
    Liljeqvist, Maria
    et al.
    Umeå University.
    Sundkvist, Jan-Eric
    Boliden Mineral AB, Boliden, Sweden.
    Saleh, Amang
    Boliden Mineral AB, Boliden, Sweden.
    Dopson, Mark
    Umeå University.
    Low temperature removal of inorganic sulfur compounds from mining process waters2011In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 108, no 6, p. 1251-1259Article in journal (Refereed)
    Abstract [en]

    Process water and effluents from mining operations treating sulfide rich ores often contain considerable concentrations of metastable inorganic sulfur compounds such as thiosulfate and tetrathionate. These species may cause environmental problems if released to downstream recipients due to oxidation to sulfuric acid catalyzed by acidophilic microorganisms. Molecular phylogenic analysis of the tailings pond and recipient streams identified psychrotolerant and mesophilic inorganic sulfur compound oxidizing microorganisms. This suggested year round thiosalt oxidation occurs. Mining process waters may also contain inhibiting substances such as thiocyanate from cyanidation plants. However, toxicity experiments suggested their expected concentrations would not inhibit thiosalt oxidation by Acidithiobacillus ferrivorans SS3. A mixed culture from a permanently cold (4-6 degrees C) low pH environment was tested for thiosalt removal in a reactor design including a biogenerator and a main reactor containing a biofilm carrier. The biogenerator and main reactors were successively reduced in temperature to 5-6 degrees C when 43.8% of the chemical oxidation demand was removed. However, it was found that the oxidation of thiosulfate was not fully completed to sulfate since low residual concentrations of tetrathionate and trithionate were found in the discharge. This study has demonstrated the potential of using biotechnological solutions to remove inorganic sulfur compounds at 6 degrees C and thus, reduce the impact of mining on the environment.

  • 7.
    Morales, Teresita A
    et al.
    Stockholm University.
    Dopson, Mark
    Umeå University.
    Athar, Rana
    Umeå University.
    Herbert, Roger B
    Uppsala University.
    Analysis of bacterial diversity in acidic pond water and compost after treatment of artificial acid mine drainage for metal removal.2005In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 90, no 5, p. 543-551Article in journal (Refereed)
    Abstract [en]

    The microbial population of a sludge amended leaf compost material utilized for treatment of artificial acid mine drainage was studied by culture-independent molecular methods. Iron-rich and sulfurous wastewater (artificial acid mine drainage) was circulated through a column bioreactor for 16 months. After 12 months the column was inoculated with a mixed culture from an acidic pond receiving acid mine drainage from a tailings impoundment at a decommissioned site in Kristineberg, North Sweden. Hydrogen sulfide odor and the formation of black precipitates indicated that sulfate-reduction occurred in the column. 16S rDNA gene analysis by denaturing gradient gel electrophoresis, cloning, and sequencing as well as fluorescent in situ hybridization confirmed the presence of microorganisms closely related to sulfate-reducing bacteria and microorganisms from the genera Pseudoxanthmonas, Dechlorosoma, Desulfovibrio, Agrobacterium, Methylocapsa, Rhodococcus, Sulfobacillus, and some unidentified bacteria. Sulfate-reducing bacteria were found in the column bioreactor 2 weeks after inoculation, but not thereafter. This suggests they were in low abundance, even though sulfate remediation rates were significant. Instead, the population contained species similar to those previously found to utilize humic substances released from the compost material.

  • 8.
    Rzhepishevska, Olena I
    et al.
    Umeå University.
    Lindström, E Börje
    Umeå University.
    Tuovinen, Olli H
    Ohio State University, USA.
    Dopson, Mark
    Umeå University.
    Bioleaching of sulfidic tailing samples with a novel, vacuum-positive pressure driven bioreactor.2005In: Biotechnology and Bioengineering, ISSN 0006-3592, E-ISSN 1097-0290, Vol. 92, no 5, p. 559-567Article in journal (Refereed)
    Abstract [en]

    This study presents a design for a novel bioreactor that uses alternating vacuum and positive pressure cycles to transfer acidic leach solution in and out of contact with finely ground sulfidic mine tailings. These tailings constitute an environmental problem that needs experimental data to support the development of management and control strategies. A conventional stirred tank bioreactor was used as a reference system. Both bioreactors were inoculated with mixed cultures of acidophilic iron and sulfur oxidizers. The rate of the bioleaching of tailings was 0.50 +/- 0.14 g Fe/L . day in the stirred tank bioreactor and 0.17 +/- 0.05 g Fe/L . day in the novel bioreactor. Microbial populations were identified in the two-bioreactor systems by analysis of 16S rRNA genes involving amplification, denaturing gradient gel electrophoresis (DGGE), cloning, and sequencing. The inoculum contained sulfur-oxidizing Acidithiobacillus caldus and Acidithiobacillus thiooxidans, iron oxidizers from the genera Leptospirillum and Ferroplasma, and a chemoorganotrophic Alicyclobacillus sp. During bioleaching of the tailings, the microbial populations in both bioreactors were similar to the inoculum culture, except that At. thiooxidans outgrew At. caldus. Sequences consistent with a Sulfobacillus sp. were amplified from both bioreactor samples although this bacterium was initially below the level of detection in the inoculum. After prolonged operation, Ferroplasma acidiphilum and an uncultured bacterium related to the CFB group were also detected in the novel bioreactor, whereas Sulfobacillus sp. was no longer detected. The novel bioreactor has potential uses in other areas of environmental biotechnology that involves periodic contact of liquids with solid substrates.

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