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MCB 3020, Spring 2005 Chapter 15: Microorganisms in the Environment

MCB 3020, Spring 2005 Chapter 15: Microorganisms in the Environment. Today:. I. Microbial impact on environment II. Photosynthesis III. Methanogenesis IV. Nitrogen fixation. I. Microbial Impact on the Environment Some examples:. Photosynthesis. Biodegradation

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MCB 3020, Spring 2005 Chapter 15: Microorganisms in the Environment

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  1. MCB 3020, Spring 2005 Chapter 15: Microorganisms in the Environment

  2. Today: I. Microbial impact on environment II. Photosynthesis III. Methanogenesis IV. Nitrogen fixation

  3. I. Microbial Impact on the Environment Some examples: Photosynthesis Biodegradation wastewater treatment landfill and toxic waste degradation Methane production: sewage treatment, landfills; cow rumen; greenhouse gas Nitrogen fixation (N2 --> NH3) Nitrification, denitrification

  4. Interaction of organisms on earth Solar energy (ultimate source of energy) Primary producers (plants, photosynthetic microbes) Decomposers (nonphotosynthetic bacteria, fungi) Consumers (herbivores, carnivores)

  5. II. Photosynthesis hv  C6H12O6 6 CO2 + 6 H2O + 6 O2 The synthesis of chemical compounds like glucose using energy from light.

  6. A. Overview of photosynthesis • occurs in plants, algae (eukaryotic), and cyanobacteria (prokaryotic) • makes organic carbon (also called reduced carbon or “fixed” carbon) • makes ATP and NAD(P)H (reductant) to synthesize organic carbon

  7. Two sets of reactions are involved in photosynthesis • Light reactions: light energy is converted to chemical energy in the form of ATP and reductant [NAD(P)H] Dark reactions (light-independent): chemical energy is used to reduce CO2, usually to the level of a sugar •

  8. Light reactions generate ATP and NADPH. Dark reactions use ATP and NADPH to reduce CO2 to carbohydrate (glucose). Oxygenic photosynthesis 6 H2O + hv 6 O2 Light reactions 12 H+ + 12 e- ATP, reductant C6H12O6 Dark reactions 6 CO2

  9. B. Light reactions of photosynthesis How do plants and microbes capture the energy of light? alga cyanobacterium Using pigments like chlorophyll

  10. Chlorophyll The main pigment for harvesting light energy by photosynthesis Located in photosynthetic membranes

  11. Chlorophyll R N N Mg N N N O R pyrrole R porphyrin or “magnesium tetrapyrrole” [cf. cytochromes (Fe), vitamin B12 (Co)] TB

  12. Arrangement of chlorophyll in membranes 200-300 light harvesting chlorophyll molecules reaction center (RC) photosynthetic membrane TB

  13. Anoxygenic photosynthesis • does not produce O2 Oxygenic Photosynthesis hv  C6H12O6 6 CO2 + 6 H2O + 6 O2 • cyanobacteria (prokaryotic) • photosynthetic algae (eukaryotic) • plants (eukaryotic) • “purple” and “green” bacteria

  14. C. Anoxygenic photosynthesis 1. overview 2. components 3. electron flow 4. membrane arrangement and ATP synthesis TB

  15. 1. Overview (anoxygenic PHS) Light PMF + ATP Used by purple and green bacteria + reductant Photophosphorylation use of light energy to make proton gradient for ATP synthesis TB

  16. 2. Components Reaction center Chlorophyll Bacteriopheophytin (Bph) Quinones (Q) Quinone pool Cytochromes (Cyt) TB

  17. 3. Electron flow in anoxygenic PHS reaction center (RC) Bph -1.0V QA QB NAD(P)+ Q pool NAD(P)H cyt. bc1 cyt. c2 H2S, SO +0.5V Midpoint potential P870* light energy P870 TB

  18. Sometimes reductant (i.e.NAD(P)H) is made using some of the electron carriers of anoxygenic photosynthesis. In this case, electrons must be supplied by an outside source like H2S (but not water!) TB

  19. 4. Membrane arrangement H+ H+ c2 c2 RC Q Q bc1 LH Bph Q Q Q Pi H+ ATP ADP H+ TB

  20. How is ATP made by photophosphorylation? • proton motive force (PMF) for ATP synthesis is generated when electrons are transferred from the Q pool to cytbf. • ATP is made when PMF is dissipated using ATP synthase.

  21. D. Oxygenic photosynthesis 1. overview 2. components 3. electron flow 4. photophosphorylation TB

  22. 1. Oxygenic photosynthesis: overview ATP Light + + PMF H2O + + NAD(P)H NAD(P)+ + O2 Algae, cyanobacteria, higher plants TB

  23. 2. Components Photosystem II (P680) Photosystem I (P700) Plastocyanin (PC) Quinone pool Cytochromes (Cyt) TB

  24. 3. Electron flow in oxygenic PHS P700* -1V FeS Fd P680* Ph NADP+ NADPH cyclic electron flow QA QB Q pool Cyt bf P700 PC P680 2e- + 2 H+ + 1/2 O2 H2O TB +1V water-splitting reaction

  25. 4. Photophosphorylation use of light energy to make proton gradient for ATP synthesis Note: The membrane organization and ATP synthesis are generally similar to anoxygenic photosynthesis

  26. In eukaryotes, photophosphorylation occurs in the chloroplast ADP + Pi ATP H+ H+ H+ stroma thylakoid

  27. E. Dark reactions of photosynthesis (light-independent reactions) CO2 reduction (CO2 fixation) to form organic matter uses ATP and NADPH made in light reactions to reduce CO2 Dark reactions can occur in the light, but do not require light.

  28. Autotrophs Organisms that use CO2 as their primary carbon source. Many are primary producers in ecosystems.

  29. Calvin cycle reductive pentose phosphate pathway uses ATP and NADPH to fix CO2 6 CO2 + 12 NADPH + 18 ATP  fructose 6-P + 12 NADP+ + 18 ADP + 17 Pi TB

  30. Key enzyme of the Calvin cycle: Ribulose bisphosphate carboxylase (RubisCo) first enzyme in the Calvin cycle CO2 + ribulose bisphosphate  two 3-phosphoglyceric acids TB

  31. Subsequent reactions (after RubisCo): In a series of reactions requiring ATP, NADPH, and molecular rearrangements, fructose 6-phosphate is produced from phosphoglyceric acid ultimately, glucose can be made TB

  32. Photosynthesis review • energy from sunlight • chlorophyll (captures light energy) • ATP made by photophosphorylation • NADPH • CO2 reduced to carbohydrates via RubisCo and Calvin cycle Result: sugar from light, water, air

  33. III. Methanogenic Archaea a diverse group of strict anaerobes that produce methane as a catabolic end-product. CH4

  34. A. Methanogenic ecosystems wastewater treatment facilities, landfills, sediments, rumen, digestive tracts, anaerobic microenvironments B. Methanogenic growth substrates H2 + CO2 formate, methanol, methylamines, acetate

  35. The anaerobic food chain (landfill, rumen, etc.) Polymers (polysaccharides, lipids, proteins) polymer degrading microbes Monomers (sugars, fatty acids, amino acids) fermentation by microbes acetate H2 + CO2 CH4+ CO2 CH4 methanogens TB

  36. C. The unusual coenzymes of methanogenesis. 1. Methanofuran CH2NH2 R OCH2 O a formyl group carrier

  37. 2. Methanopterin R HN O H CH N HN CH3 N N CH3 NH2 H C1 carrier functionally analogous to folate Carriers C1 groups at several oxidation states

  38. 3. Factor F430 N N Ni N N a nickel tetrapyrrol Methyl carrier

  39. 4. Factor F420 R HO N N O NH O a 5-deazaflavin functions as an electron carrier

  40. 5. Coenzyme B O CH3 O = = HOPOCHCHNHCCH2CH2CH2CH2CH2CH2SH HO COOH an electron carrier with an active sulfhydryl group

  41. 6. Coenzyme M HS-CH2-CH2 SO3– a methyl carrier CH3-S-CH2-CH2 SO3– methyl-CoM

  42. D. The pathway of methanogenesis from CO2 CO2 H2 MF-CHO MF = methanofuran MP-CHO MP = methanopterin F420 H2 MP-CH2OH

  43. H2 F420 MP-CH3 CoM-CH3 CoB-SH CH4 CoB-SS-CoM + H2 CoB-SH + HS-CoM

  44. IV. Nitrogen fixation • Use of nitrogen gas (N2) as a nitrogen source. • Occurs in prokaryotes only • Some prokaryotes enter into symbiotic relationships with leguminous plants TB

  45. A. Nitrogenase Fe protein MoFe protein Enzyme that catalyzes the reduction of N2 to NH3.

  46. 1. Overall reaction of nitrogenase Nitrogenase 2NH3 + H2 + 16 ADP +16 Pi N2 + 8H+ + 8e- +16 ATP The formation of H2 is a by-reaction TB

  47. The microbial nitrogen cycle N2 nitrogen fixation denitrification NO3- NH3 nitrification

  48. Study objectives 1. Know the details of photosynthesis and be able to compare and contrast oxygenic and anoxygenic photosynthesis. 2. Compare and contrast photophosphorylation, oxidative phosphorylation, and substrate level phosphorylation. How is the proton motive force made? Where does photosynthesis occur in eukaryotes? 3. What is the role of water in oxygenic photosynthesis? Does water play the same role in anoxygenic photosynthesis? 4. Define autotroph. What is the purpose of the Calvin cycle? What types of organisms use this cycle? Know the reaction catalyzed by Rubisco. How is glucose made in the dark reactions of photosynthesis? 5. Be able to describe how a photosynthetic cell makes sugar from air, water, and light. What is the purpose of the ATP and NADPH? How are they made? How are they used in the production of sugars from CO2? 6. What are methanogenic Archaea? Where are they found? What are the substrates for methanogenesis? 7. Understand the role of methanogens in the anaerobic food chains of rumen, landfills, wastewater treatment facilities, and other anaerobic ecosystems.

  49. 8. Name the unusual coenzymes of methanogenesis and their general functions. 9. Define nitrogen fixation. What organisms are capable of nitrogen fixation? What is the reaction of nitrogenase? Note that it requires reductant and ATP. 10. Distinguish between nitrification and denitrification. (See last slide.)

  50. MCB 3020 Spring 2004 Chapter 11: Industrial and Environmental Microbiology

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