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MICRB 265 General Microbiology

MICRB 265 General Microbiology. Doug McFarlane Lecture 16 –Sulfate-Reducing Bacteria. Announcements. Midterm exam – Wednesday, Oct. 24 (in class) Help sessions: Monday, Oct. 22, 2:00 Tuesday, Oct. 23 (mole day!), 1:00 By appointment, or office hours Confusion:

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MICRB 265 General Microbiology

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  1. MICRB 265 General Microbiology Doug McFarlane Lecture 16 –Sulfate-Reducing Bacteria

  2. Announcements • Midterm exam – Wednesday, Oct. 24 (in class) • Help sessions: Monday, Oct. 22, 2:00 • Tuesday, Oct. 23 (mole day!), 1:00 • By appointment, or office hours • Confusion: • Fermentations: can be done by aerotolerant anaerobes (like LAB) or by facultative aerobes (like E. coli)

  3. Last Lecture • Chemoorganoheterotrophs • Fermentations (cheese, etc.) • Obligate anaerobes, anaerobic Rs – SRB, metal corrosion

  4. Chemoorganoheterotrophs

  5. Today’s Lecture • Chemoorganoheterotrophs • Fermentations (cheese, etc.) • Obligate anaerobes, anaerobic Rs – SRB, metal corrosion • Chemolithoautotrophs • Sulfur-oxidizing bacteria • Iron-oxidizing bacteria • Methanogens – cow rumens and global warming

  6. Assimilative vs. Dissimilative SO42- reduction Dis: use SO42- as TEA

  7. Assimilative vs. Dissimilative • Gives enzymes a handle on SO42-

  8. Case Study #3 • Chemoorganoheterotrophs • Obligate anaerobes (anaerobic respiration) • Metal corrosion • Sulfate-reducing bacteria (SRB) • 17.15 in Brock

  9. Sulfate-Reduction 2e- 2e- 2e- 2e- • SO42- SO32- S2O32-  S0  S2- • Diverse metabolism – SRB • Some are chemoorganoheterotrophs • Most can use H2 as electron source • Chemolithoheterotrophs • Some can grow autotrophically • Some are facultative respirers • Slow growers sulfate sulfite thiosulfate sulfur sulfide

  10. Redox

  11. Metabolism – SRB Diverse!

  12. Metabolism – SRB

  13. Corrosion Process • Fermenters  lactate, etc. • SRB: lactate  pyruvate + H2 • H2 used by H2ase  PMF, ATP • TEA is SO42- S2- • Fe0 Fe2+ (spontaneous electrochemical reaction) • Fe2+ + S2-  FeS

  14. Bug #12 – Desulfovibrio vulgaris • Bacteria; Gram negative vibrio • Habitat: anaerobic sediments, sewage treatment plants, soil, buried pipes • First anaerobic respiration chain studied • Usually lives in biofilms

  15. Bug #12 – Desulfovibrio vulgaris • Has unusual hydrogenase in periplasm • Industrial importance: • Accelerates anaerobic corrosion of metals • Souring of oil and gas (production of H2S)

  16. Chemoautotrophs • Sulfur-oxidizing bacteria – deep sea ecosystems • 11E: pp. 337-338, 550-552 • 10E: pp. 360-362, 568-571 • Iron-oxidizing bacteria – acid mine drainage/ bioleaching • 11E: pp. 553-555, 644-649 • 10E: pp. 571-572, 666-669 • Methanogenesis – cow rumen, global warming • 11E: pp. 426-430, 564-568, 634-637 • 10E: pp. 453-455, 583-587, 654-658

  17. Chemoautotrophs • Auto: fix CO2 as a carbon source • Chemo: use a chemical for energy (usually an inorganic chemical) • Most are aerobic (notable exception: methanogens) • Most inhabit unusual environments

  18. Case Study #4 – Sulfur-Oxidizing Bacteria • Sulfur-oxidation pathway: • S2-  S0  S2O32-  SO32- SO42- • Note similarity to SRB • Electron source? 2e- 2e- 2e- 2e- sulfide sulfur thiosulfate sulfite sulfate

  19. Sulfur-Oxidizing Bacteria • Some SOB save up S0 as granules (e.g. Thiomargarita namibiensis) • TEA is usually O2 (aerobic Rs) • Sulfur oxidation generates energy (chemotrophy) • Energy used to fix CO2 (autotrophy)

  20. Sulfur-Oxidizing Bacteria • Two main groups: • Neutral pH • Incomplete oxidation (often accumulate S0) • E.g. hydrothermal vent ecosystems • Acidic pH (acidophiles) • Complete oxidation – generate H2SO4 • E.g. Thiobacillus sp. • Some are Fe2+ oxidizers (later; acid mine drainage and bioleaching)

  21. Hydrothermal Vents • Deep-sea ecosystems • Life without light… • Primary producers; food chains • Autotrophs vs. heterotrophs • Clams, tubeworms, shrimp, crab

  22. 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…

  23. Case Study #5 – Iron-Oxidizing Bacteria • Oxidize ferrous ion (Fe2+) to ferric ion (Fe3+) • Tend to live in acidic environments (acidophiles) • Acid makes Fe2+ available (otherwise precipitates easily) • E.g. Acidothiobacillus ferrooxidans

  24. Iron-Oxidizing Bacteria • Relatively easy to generate DpH (PMF) • Need to maintain internal environment near neutral pH • Short electron transport chain – insufficient for generating PMF • Uses O2 as TEA  H2O, thus taking H+ out of cytoplasm (neutralizing pH)

  25. IOB: Autotrophy • Autotrophy requires NADPH+ in order to reduce (fix) CO2 • Using the Calvin cycle (BIOL 107) • NADPH+ is produced by running the ETC “backwards” or “uphill” • Uses PMF to force electrons against the normal redox path up to NADPH+

  26. Next Lecture • Metabolic Diversity – case studies • Chemoautotrophs • Iron-oxidizing bacteria • Methanogens

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