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Case Study: Sulfur and Iron Oxidizing Bacteria

Case Study: Sulfur and Iron Oxidizing Bacteria. Chemolithotrophs Most are also autotrophs Use sulfur and/or iron compounds as an energy and electron source Brock: 12E: 15.4, 20.10, 20.11 11E: pp. 550-555, 644-649. Sulfur Oxidation. Sulfur-oxidation pathway:

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Case Study: Sulfur and Iron Oxidizing Bacteria

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  1. Case Study: Sulfur and Iron Oxidizing Bacteria • Chemolithotrophs • Most are also autotrophs • Use sulfur and/or iron compounds as an energy and electron source • Brock: • 12E: 15.4, 20.10, 20.11 • 11E: pp. 550-555, 644-649

  2. Sulfur Oxidation • Sulfur-oxidation pathway: • S2-  S0  S2O32-  SO32- SO42- • Note: reverse of SRB • Electron source? • Sulfur compounds releasing e-! • Chemolithotrophy 2e- 2e- 2e- 2e- sulfide sulfur thiosulfate sulfite sulfate

  3. Iron Oxidation e- • Fe2+  Fe3+ • Also chemolithotrophy

  4. Sulfur-Oxidizing Bacteria (SOB) • 2 main groups: • Acidophiles • Also tend to be iron-oxidizing bacteria • Live around metal/sulfur ores • Produce sulfuric acid as a metabolic by-product • Non-acidophiles • Live in aqueous environments • E.g. those living at the bottom of the ocean near hydrothermal vents

  5. Acidophilic SOB • Complete oxidation of H2S results in production of H2SO4 • Most are also IOB Thiobacillus ferrooxidans microbewiki.kenyon.edu/index.php/Thiobacillus

  6. Antimicrobial Concrete • http://www.zeomic.co.jp/english/05_01_zeomighty.html

  7. Non-Acidophilic SOB • Halothiobacillus neapolitanus - arrows showing carboxysomes (contain high levels of Calvin cycle enzymes) • Achromatium cells - sulfur granules and CaCO3

  8. Filamentous SOB • Beggiatoa - from sewage treatment plant • Note the sulfur granules • Recall Thiomargarita namibiensis

  9. Sulfur-Oxidizing Bacteria • Some SOB store S0 as granules (e.g. Thiomargarita namibiensis) • Use granules as a reserve energy source for when H2S levels diminish

  10. Hydrothermal Vents • Deep-sea ecosystems • Life without light… • Primary producers - bottom of the food chain • Clams, tubeworms, shrimp, crab

  11. Hydrothermal Vents – SOB • Free-living; e.g. Thiobacillus hydrothermalis • Endosymbionts; e.g. tube worms house endosymbiotic SOB in tissue called trophosome • Epibionts (symbionts on external surface) • Other dark places…

  12. SOB - Metabolism • Most use aerobic Rs (O2 as TEA) • Some can use NO3- as TEA Reverse electron flow - e- enter the ETC at too high a redox potential to produce NADH directly. Reverse electron flow allows e- to be transferred against their potential to produce NADH for CO2 fixation

  13. IOB - Habitat • Most are obligate acidophiles • Acidic environment allows Fe2+ (energy and electron source) to exist in aqueous solution • Must maintain neutral cytoplasm • Live in coal mines, iron mines, ores with iron and sulfides (e.g. FeS - iron pyrite)

  14. IOB - Metabolism • PMF maintained by neutralizing cytoplasm (not pumping protons) • Using H+ with O2 to make H2O • Reverse e- flow • Autotrophy • Calvin cylce

  15. SOB/IOB: Autotrophy • Autotrophy requires NADPH+ in order to reduce (fix) CO2 • Using the Calvin cycle • NADPH+ is produced by running the ETC “backwards” or “uphill” • Uses PMF to force electrons against the normal redox path up to NADPH+

  16. Bug #13: Acidithiobacillus ferrooxidans • Bacteria; Gram negative rod • Metabolism: Iron- and sulfur-oxidizer; chemolithoautotroph • Uses reverse ETC to generate NADPH+ for CO2 fixation (via Calvin cycle) • Facultative anaerobe; obligate respirer (O2 or NO3-)

  17. Bug #13: Acidithiobacillus ferrooxidans • Habitat: acidophile; associated with metal ores (biofilms on ores) • Responsible for acid mine drainage • Can be used for bioleaching

  18. Acid Mine Drainage • Chemical: • FeS2 + 3.5 O2 + H2O  Fe2+ + 2 SO42- + 2 H+ • Biological: • 2 Fe2+ + ½ O2 + 2 H+  2 Fe3+ + H2O • Chemical: • FeS2 + 14 Fe3+ + 8 H2O  15 Fe2+ + 2 SO42- + 16 H+ • High conc. H+ dissolves other minerals (e.g. Al3+) - TOXIC

  19. Acid Mine Drainage Fe(OH)3

  20. Bioleaching • Upgrading low-grade ores – solubilizing metal ions for recovery by electroplating • Sulfide ores  sulfide is oxidized, acid is produced, metal ions released • E.g. Cu, U, Au, Pb • Part of the process involves iron and sulfur-oxidizing bacteria

  21. Bioleaching

  22. Bioleaching

  23. Bioleaching

  24. Bioleaching Chemistry • Direct oxidation of metal: • Cu2S + ½ O2 + 4 H+ CuS + Cu2+ + H2O • Oxidation of sulfur: • CuS + 2 O2 Cu2+ + SO42- • Indirect oxidation of Fe2+: • Fe2+ + ½ O2 + 2 H+ Fe3+ + H2O • CuS + 8 Fe3+ + 4H2O  Cu2+ + SO42- + 8 Fe2+ + 8 H+ • Scrap iron used to plate out soluble Cu2+: • Fe0 + Cu2+ Cu0 + Fe2+

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