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Case Study - Methanogens

Case Study - Methanogens. “Methane generators” Lab #10 Brock: 12E-17.4, 21.10, 24.10 11E-13.4, 17.17, 19.10 All are Archaea Genera have prefix “ Methano- ” E.g. Methanocaldococcus jannaschii Habitat: obligate anaerobes; rumen, sediments, landfills, colon, sewage. Habitat.

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Case Study - Methanogens

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  1. Case Study - Methanogens • “Methane generators” • Lab #10 • Brock: 12E-17.4, 21.10, 24.10 • 11E-13.4, 17.17, 19.10 • All are Archaea • Genera have prefix “Methano-” • E.g. Methanocaldococcusjannaschii • Habitat: obligate anaerobes; rumen, sediments, landfills, colon, sewage

  2. Habitat

  3. Volta Experiment

  4. Metabolism • Very slow, inefficient • CO2 is a very poor TEA

  5. Redox

  6. Substrates 12E:17.6 Three main categories of methanogens according to energy and electron sources

  7. Chemoorganoheterotrophy • Type 1 - Formic acid: • 4 HCOOH  CH4 + 3 CO2 + 2H2O (1:3) • Type 2 - Methylotrophic: • 4 CH3OH  3 CH4 + CO2 + 2 H2O (3:1) • Type 3 - Acetoclastic: • CH3COOH  CH4 + CO2 (1:1) • Part of the substrate used for energy, part for biosynthesis (biomass)

  8. Methanogens – Metabolism • E.g. Type 1 • CO2 + 4 H2 CH4 + 2 H2O (energy) • 8 H2 + 3 CO2 + CoA  acetyl-CoA + CH4 + 4 H2O + H+ (autotrophy - biomass) • CO2 serves as C-source and TEA

  9. Energy Production • Anaerobic Rs • No substrate-level phosphorylation • Unique series of co-factors used to reduce CO2 – last step produces PMF

  10. ETC

  11. ETC - Membrane

  12. CO2 Fixation • Via acetyl-CoA pathway • Unique type – methanogens only • Complex series of coenzymes, not found in other organisms

  13. The Rumen • An example of: • Microbial ecology • Animal-microbe symbiosis • Brock: 12E-24.10; (11E-19.11) • Digestive system in ruminants • Ruminants: two step digestive process (chew their cud) • Cattle, goats, sheep, camels, llamas, giraffes, bison, yaks, water buffalo, deer, wildebeest

  14. Cow

  15. Rumen • In cattle: ~ 100 L • 39oC; pH 5.8-6.8; anaerobic • Extensive biomass: • 1010 – 1011 cells/mL • 100 L (100,000 mL) • = 1016 – 1017 microbial cells • Vs. ~ 1013 cow cells • Diverse population – “a walking anaerobic incubator” • Bacteria, Archaea, fungi, protists

  16. Rumen • Inputs: mostly cellulose • Cows do not have cellulase to break down cellulose • Digestion carried out by normal microflora

  17. Substrates Common waste products from fermenters!

  18. Cellulose Breakdown

  19. Microbes Involved • Cellulase-producers • Fibrobacter succinogenes (Gram negative rod); cell-associated cellulase; capsule to adhere • Ruminococcus albus (Gram positive coccus); extracellular cellulase • Cellulose (and starch)  cellobiose and glucose

  20. Microbes Involved • Fermenters • E.g. E. coli, Bacteroides ruminicola (Gram negative rod), thousands of others (Bacteria, Archaea, yeasts, protists) • A variety of fermentation types, a variety of products

  21. Fermentation Products • Ethanol, alcohols • CO2 and H2 • Volatile fatty acids (VFAs) • Formic acid, acetic acid, propionic acid, butyric acid, etc. • Smell! • Some absorbed by cow, much is used by methanogens

  22. Microbes Involved • Methanogens • Convert CO2 and H2 to CH4 • Convert small VFAs (such as formate) to CH4 • Cow burps: ~ 65% CO2, 35% CH4 • Cannot use larger VFAs directly --> syntrophy

  23. Syntrophy • Two organisms combine their metabolic capabilities to catabolize a substance not capable of being catabolized by either one alone • VFAs (e.g. propionate, butyrate)  smaller compounds (formate, CO2 and H2)  used by methanogens

  24. Microbes Involved • Synotrophic bacteria • E.g. Syntrophomonas spp. • VFAs  formic acid, acetic acid, H2, etc. • Thermodynamically unfavourable • Methanogens scavenge up all the H2, thereby pulling reaction to the right (LeChatelier’s principle) • Interspecies hydrogen transfer

  25. Benefits to the Cow • VFAs absorbed through the rumen wall  carbon and energy source • Microbial biomass digested by the cow  nutrients (proteins, amino acids, nucleic acids, carbon and nitrogen source) • Vitamins

  26. Net Reaction: • Cellulose  CO2 + CH4 + biomass (cow and microbial; poop) • Cows produce ~ 100-500 L gas per day • 35% CH4, 65% CO2 • Currently about 1.5 billion cows

  27. Greenhouse Gases and Global Warming • Al Gore and the IPCC win Nobel Peace Prize • http://www.cbc.ca/world/story/2007/10/12/nobel-peace.html?ref=rss • Methane is about 20-25x worse than CO2 (but present in much lower amounts)

  28. Global Methane • Rates

  29. Minimizing Ruminant Methane Production • Change cattle feed to lower methane production • Probiotics for cows (kangaroo poo news article) • Eat less beef…

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