Daniel Kupka

Oxidation of elemental sulfur, tetrathionate and ferrous iron by the psychrotolerant Acidithiobacillus strain SS3.

Mesophilic iron and sulfur-oxidizing acidophiles are readily found in acid mine drainage sites and bioleaching operations, but relatively little is known about their activities at suboptimal temperatures and in cold environments. The purpose of this work was to characterize the oxidation of elemental sulfur (S(0)), tetrathionate (S4O6(2-)) and ferrous iron (Fe2+) by the psychrotolerant Acidithiobacillus strain SS3. The rates of elemental sulfur and tetrathionate oxidation had temperature optima of 20 degrees and 25 degrees C, respectively, determined using a temperature gradient incubator that involved narrow (1.1 degrees C) incremental increases from 5 degrees to 30 degrees C. Activation energies calculated from the Arrhenius plots were 61 and 89 kJ mol(-1) for tetrathionate and 110 kJ mol(-1) for S(0) oxidation. The oxidation of elemental sulfur produced sulfuric acid at 5 degrees C and decreased the pH to approximately 1. The low pH inhibited further oxidation of the substrate. In media with both S(0) and Fe2+, oxidation of elemental sulfur did not commence until all available ferrous iron was oxidized. These data on sequential oxidation of the two substrates are in keeping with upregulation and downregulation of several proteins previously noted in the literature. Ferric iron was reduced to Fe2+ in parallel with elemental sulfur oxidation, indicating the presence of a sulfur:ferric iron reductase system in this bacterium.

Degradation of Reactive Black 5 by electrochemical oxidation

Degradation of commercial grade Reactive Black 5 (RB5) azo dye by chemical and electrochemical treatment was examined using a dimensionally stable anode and stainless steel cathodes as electrode materials, with NaCl as supporting electrolyte. The electrochemical treatment was compared to the chemical treatment with hypochlorite generated by electrolysis. The compounds present in the commercial grade RB5 azo dye and the products of its electrochemical degradation were separated using ion-pairing high performance liquid chromatography on reversed phase. The separated species were detected by diode array detector and electrospray ionization mass spectrometry. A suitable ion-pairing reversed phase HPLC-MS method with electrospray ionization for the separation and identification of the components was developed. The accurate mass of the parent and fragment ions were used in the determination of the empirical formulas of the components using the first-order mass spectra. Structural formulas of degradation products were proposed using these information and principles of organic chemistry and electrochemistry.

Deferrization of Kaolinic Sand by Iron Oxidizing and Iron Reducing Bacteria

Iron oxidizing bacteria Acidithiobacillus ferrooxidans, iron reducing bacteria Acidiphilium spp. and their mixture were applied for leaching of iron impurities from quartz sand. The bacterial leaching was carried out in order to decrease the amount of colouring iron oxides and to improve the technological properties of the raw material. Mineralogical analysis confirmed the presence of siderite, iron-bearing muscovite and various amorphous and crystalline forms of iron oxides occurring both free and coating siderite and quartz particles. Mössbauer spectroscopy revealed various oxidation and magnetic states of iron ions, with the prevalence of reduced ionic species. Highest extraction of iron was achieved with pure culture of iron-reducing bacteria with ferrous iron as dominant species in the leaching liquor. Surprisingly, iron oxidizing bacteria caused passivation of the surface of iron-bearing minerals, resulting in the depression of iron leaching in comparison with abiotic control. Ferric iron was major species in the leaching solution containing the mixed culture of iron-oxidizing and iron-reducing bacteria. The mixture was far less efficient in iron extraction than pure culture of iron-reducing bacteria.

Sulfur Oxidation and Coupled Iron Reduction at Low Temperatures

The purpose of this work was to characterize elemental sulfur oxidation by a psychrotrophic Acidithiobacillus ferrooxidans culture that originated from an AMD-impacted surface soil in a permafrost area in northern Siberia. In this work, the iron-oxidizing culture was cultivated with elemental sulfur with and without Fe2+ or Fe3+ in flasks on a shaker to avoid oxygen limitation.

A comparative electrophoretic light scattering study of various strains of Thiobacillus ferrooxidans

No significant strain-specific differences were found in the shape and position of the pH-dependent electrophoretic mobility curve obtained for various strains of Thiobacillus ferrooxidans under equal conditions of growth, suggesting similarities in their surface charge development.

Iron Oxidation and Bioleaching Potential at Low Temperatures

Objectives The purpose of this study was to assess iron oxidation and prospects of bioleaching at low temperatures relevant in arctic and boreal environments. Iron-oxidizing acidophiles were enriched at 5°C from samples from a Ni-Cu mine site (northern Siberia) and the kinetics of iron oxidation by one of the isolates (strain SS3) was evaluated at low temperatures. Additionally, low temperature bioleaching was tested with either a pure (strain SS3) or mixed (T7 mix) culture in stirred tank reactors and column reactors, respectively. Results The oxidation kinetics at 5°C could be described with the first order rate expression. The rate of iron oxidation at 5°C by SS3 was nearly as fast as that at 30°C by a mesophilic reference strain. Iron precipitates in cultures grown at 5°C were mixtures of schwertmannite and jarosite, whereas jarosite was the exclusive solid phase at 30°C. The bioleaching potential of isolate SS3 was tested in stirred tank reactors containing pyrite, pyrite-arsenopyrite, and chalcopyrite concentrates. With SS3, the leaching rates in stirred tank reactors were much lower at 5°C than at 30°C due to slow chemical oxidation rates of sulfide minerals by Fe

Reduction of Soluble and Solid Ferric Iron by Acidiphilium SJH

Facultative Fe(III)-reducing bacterium Acidiphilium SJH was incubated in media with ferric iron under various conditions with respect to oxygen availability for the growing cells. The bacteria oxidized organic substratum to carbon dioxide using oxygen and ferric iron as terminal electron acceptors. Ferric iron reduction was observed in all incubation modes. The distribution of reducing equivalents from the oxidation of organic carbon for the reduction of both O2 and Fe(III) was evaluated from CO2 production rate and O2 consumption rate. In fully aerobic conditions approximately 10 % of CO2 produced was coupled with reduction of Fe(III) as terminal electron acceptor. Under aerobic conditions, the ratio of CO2 produced to O2 consumed remained unaffected in a broad concentration range of dissolved oxygen. In the course of oxygen limitation (microaerobic conditions) the molar CO2 to O2 ratio increased from approx. 1 to 2 and even much more with respect to oxygen transfer rate during incubation. On the other hand no bacterial growth and extremely slow iron reduction was observed in obligatory anaerobic conditions in a reactor purged with either pure or CO2-enriched nitrogen.

Synthesis of the cytotoxic phytosphingosines and their isomeric analogues

A straightforward synthesis of l-lyxo- and l-xylo-phytosphingosine along with their isomeric analogues has been accomplished. The salient features of this approach are the utilization of [3,3]-sigmatropic rearrangements to install a C-N bond and application of a late stage Wittig or OCM reaction to incorporate the hydrophobic chain unit. The final compounds were evaluated regarding their ability to alter both leukaemia and solid tumor cancer cells viability.