1 / 39

Microbial Metabolism— Procuring Energy!

Microbial Metabolism— Procuring Energy!. Metabolic diversity. Energy flow. For Energy. For Energy. Carbon Flow for Anabolism.

butch
Download Presentation

Microbial Metabolism— Procuring Energy!

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Microbial Metabolism—Procuring Energy!

  2. Metabolic diversity Energy flow For Energy For Energy Carbon Flow for Anabolism

  3. Key PointsDissimulative metabolism—Reduction of chemicals for energy—much material must be used to achieve sufficient energy for growthAssimilative metabolism—Reduction of chemicals for biomass—the cell only uses as much starting material as required

  4. Anaerobic Respiration—molecular oxygen does NOT serve as an electron acceptor but energy (ATP) is produced via chemiosmosis NO3-   N2 or SO4-- H2S or CO2   CH4 1. Nitrate    Nitrogen gas 2. Sulfate  Hydrogen Sulfide gas 3. Carbon dioxide    methane 1,2. Standard electron transport, 3.membrane bound enzymes Both generate proton gradient required for PMF

  5. In anaerobic metabolism Nitrate or Sulfate serve as terminal electron acceptors at the end of the electron transport chain NADHNAD  • FADH • FAD Co Q      I II III Thus under anaerobic conditions some organisms can still obtain high levels of energy IV Mixotrophs, Energy from oxidation of organic chemicals inorganic chemicals are reduced. NO3-   N2 SO4-- H2S

  6. Denitrification (Nitrate reduction)Some Pseudomonas, Bacillus and Thiobacillus spp. NR NR NcOR NsOR NO3- NO2-  NO  N2ON2 Gases to atmosphere Nitrate reduction is mediated by enzymes 1. nitrate reductase (NR) 2. nitric oxide reductase (NcOR) 3. nitrous oxide reductase (NsOR)

  7. Significance of denitrification 1. Agriculture: soil nitrate that could be fixed to ammonia and assimilated by plants are reduced to atmospheric nitrogen and lost from the soil (however—nitrogen fixing bacteria can restore atmospheric nitrogen to the soil as part of the overall nitrogen cycle) • Acid rain: atmospheric nitrous oxide is converted to nitric • oxide via sunlight. This combined with nitric oxide released via • denitrification reacts with ozone to form nitrite that returns to the • earth as acid rain. • Sewage treatment plants (water purification): Denitrifying • bacteria are added to the sewage to convert nitrate to atmospheric • nitrogen to remove nitrogen that would otherwise promote the • growth of algae

  8. Significance of denitrification NR NR NcOR NsOR NO3- NO2-  NO  N2ON2 Gases to atmosphere 1. Agriculture: soil nitrate that could be fixed to ammonia and assimilated by plants are reduced to atmospheric nitrogen and lost from the soil (however—nitrogen fixing bacteria can restore atmospheric nitrogen to the soil as part of the overall nitrogen cycle)

  9. Significance of denitrification NR NR NcOR NsOR NO3- NO2-  NO  N2ON2 N2O NO2- NO • Acid rain: atmospheric nitrous oxide is converted to nitric • oxide via sunlight. This combined with nitric oxide released via • denitrification reacts with ozone to form nitrite that returns to the • earth as acid rain. NO2- sunlight NR ozone H2O Acid rain

  10. Significance of denitrification 1. Agriculture: soil nitrate that could be fixed to ammonia and assimilated by plants are reduced to atmospheric nitrogen and lost from the soil (however—nitrogen fixing bacteria can restore atmospheric nitrogen to the soil as part of the overall nitrogen cycle) • Acid rain: atmospheric nitrous oxide is converted to nitric • oxide via sunlight. This combined with nitric oxide released via • denitrification reacts with ozone to form nitrite that returns to the • earth as acid rain. • Sewage treatment plants (water purification): Denitrifying • bacteria are added to the sewage to convert nitrate to atmospheric • nitrogen to remove nitrogen that would otherwise promote the • growth of algae

  11. Sulfate ReductionBacteria responsible for this are widespread in aquatic environments ATPS APSR SR SO4-- SO3-- H2S Sulfate reduction is mediated by enzymes 1. ATP sulfurylase (ATPS) 2. APS reductase (APSR) 3. sulfite reductase (SR) Excreted into environment

  12. Significance of sulfate reduction Pollution of waters: Sulfate reducing bacteria are limited by the amount of organic starting material available in the aquatic environment which when metabolized by these bacteria provide the electrons/protons that drive the sulfate to sulfide reaction. Disposal of sewage and garbage into waters provides the organic material required for this process Sulfides are toxic to living organisms as these sulfides combine with iron centers of cytochromes and hemoglobin thus inhibiting their function N.B. Fe can serve as a detoxifying agent as they react with sulfides to produce insoluble FeS—black sediments found in aquatic environments are good indicators of pollution!!!)

  13. Carbon dioxide reduction Methanogenesis(methanogens: anaerobic archaebacteria) Glycolysis  pyruvate  FERMENTATION Formate, Acetate Lactate, Proprionate Butyrate, etc Membrane associated reactions of methanogenesis CO2 and protons (H2)     CH4 excreted Complex set of reactions that take place in the membranes of these bacteria: protons for CO2 reduction come from fermentation, methanogenesis (somewhat different from electron transport) provides proton motive force that drives the production of ATP

  14. Significance of methanogenesis Sewage treatment plants Insoluble sludge from primary treatment is degraded by a variety of anaerobic bacteria using catabolic pathways and fermentation. (we drink)

  15. Anoxic digestion of sludge • Methanogens use protons from • catabolism and fermentation to reduce • CO2 from fermentation to methane. • The methane is collected as natural gas to fuel and heat the • sewage plant or burned off.

  16. Significance of methanogenesis Digestive processes: Methanogens are found in the rumen of cows, sheep, deer etc. The caecum of horses and rabbits, the large intestines of humans, cats, dogs etc. and the hindgut of termites. • Herbivores: cows/horses/rabbits/termites • bacteria degrade cellulose to cellobiose to glucoseglycolysis • fermentation  organic acids are assimilated and CO2 and H2 are reduced to methane by methanogens Omnivores: humans/cats/dogs/pigs vast catabolic processes fermentation methanogenesis of CO2 Methane waste: Cows belch, humans expel gas and I don’t know what the termites do!!!

  17. Stop here

  18. Chemolithotrophy—obtaining energy from inorganic chemicals1. inorganic chemicals are oxidized as coenzymes in the electron transport chain are reduced.2. Oxygen serves as the terminal electron acceptor in electron transport3. Reducing power is not derived from the catabolism of organic matter to produce NADH and FADH therefore these cofactors are usually not re-oxidized in chemolithotropy4. The chemicals that are oxidized have lower energy potential than NADH, therefore more of these chemicals must be oxidized to generate equivalent proton motive force to produce ATP Chemolithotrophs tend to grow more slowly than chemo-organotrophs

  19. Chemolithotrophy X NADHNAD  • FADH • FAD Co Q      X Fe2+ Fe3+ NH4NO2- /NO3- H2S/S2O32-H2SO4 O2 H2O

  20. Sulfur and Iron oxidation(Thiobacillus thiooxidans, Thiobacillus ferrooxidans and others.) 1. Fe2+ Fe3+ ferrous iron to ferric iron 2. H2S  elemental sulfurH2SO4 hydrogen sulfide to sulfuric acid 3. S2O32-H2SO4 thiosulfate to sulfuric acid N.B. Ferric iron can often serve as an oxidizing agent Sulfuric acid greatly decreases the pH of the surrounding environment Sulfates can also be assimilated as a food source for bacteria/plants

  21. Significance of sulfur and iron oxidation Hydrothermal vents::symbiotic relationships between animals and bacteria dwelling in these niches (Thiobacillus, Thiomicrospora, Thiotrix)—clams, mussels, tube worms 1. Basalt/magma rich in minerals beneath ocean floor produce cracks in ocean floor. 2. Minerals mix with sea water and are expelled from ocean floor. Black smokers: precipitated minerals mixed with seawater/ 270-380oC

  22. Life in hydrothermal vents There is no sunlight at these depths in the ocean yet niches around the vents are robust with life. Chemolithotrophs serve as primary producers • Bacteria live in the GI tract of tube worms/ the gills of mussels • and clams. • Tube worms/mussels/clams provide CO2 as a carbon source for • the bacteria. • The bacteria oxidize hydrogen sulfide and thiosulfate to H2SO4 • for energy and reducing power and use this for the assimilation • of CO2. • 4. Wastes from bacterial metabolism feed the larger animals

  23. Significance of sulfur and iron oxidation Pollution/Acid mine Drainage (Thiobacillus and Metallogenium spp.) • Strip coal mining exposes the pyrite • (FeS2) in coal to oxygen. • 2. Bacteria oxidize ferrous iron to ferric • iron • 3. Oxidation of sulfides to sulfuric acid • greatly reduces the pH of the water • 4. Ferric iron reacts with water to form • iron III hydroxide (Fe(OH)3) which • further lowers the pH of the water • 5. Fe(OH)3 precipitates to form slimy • orange coating that covers the stream bed • (indicator for pollution) • Acid soon kills the aquatic life at the • bottom of stream bed

  24. Significance of sulfur and iron oxidation Microbial Bioremediation— Bio-leaching use of bacteria to extract pure metal from ores with low metal content Can be used to isolate almost any divalent metal: copper, uranium nickel, cobalt, tin, zinc, etc. Insoluble metal sulfides are oxidized to soluble metal sulfates i.e. Copper required for electricity is in short supply

  25. Bioremediation Similarly, sulfur/iron oxidizing bacteria can be used to isolate important fuel sources. Uranium usually found naturally as the low grade ore uranium oxide (UO2) . Thiobacillus spp. oxidize ferrous iron to ferric iron which In turn oxidizes UO2 to soluble UO2SO4 Oil recovery: recovery of petroleum and hydrocarbons from oil shales 1. Oil shales contain large amounts of carbonates and pyrites 2. Thiobacillus oxidizes the sulfur and iron in the pyrites to produce acids 3. Acids dissolve the carbonates thus increasing the porosity of the oil shales 4. Oil can be more easily recovered from these shales.

  26. Nitrification/Nitrogen oxidation by nitrifying bacteria A two step process mediated by two genera of bacteria NH4NO2- Nitrosomonas spp. ammonium to nitrite NO2- NO3- Nitrobacter spp. nitrite to nitrate N.B. 35 moles of ammonium and/or 100 moles of nitrate are required to generate enough reducing power and ATP to convert one mole of carbon dioxide into organic carbon

  27. Significance of nitrifying bacteria Agriculture: nitrifying bacteria leach nitrogen required by plants from the soil. 1. Positively charged Ammonium ions are absorbed by negatively charged clay particles present in the soil, thus retaining nitrogen 2. Negatively charged nitrites and nitrates are not absorbed by these clay particles and are leached into the groundwater A. loss of nitrogen from soil B. nitrites in the water supply are toxic 1. nitrites combine with hemoglobin to block the exchange of oxygen 2. nitrites react with amino compounds to form carcinogenic nitrosamines

  28. Oxidative and Anaerobic Photo-phosphorylation(obtaining energy from sunlight) Algae –takes place in chloroplasts Cyanobacteria –occurs in thylakoid membranes Purple bacteria/sulfur bacteria and Heliobacteria –occurs in lamellar membranes Web sites for better understanding http://www-micro.msb.le.ac.uk/video/photosynthesis.html http://www.biologie.uni-hamburg.de/b-online/chimes/photo/ebacphot.htm

  29. Photosynthetic membranes of the bacteria Lamellar membranes in a purple bacterium These membranes also arise from invagination of the cytoplasmic membrane, but instead of forming vesicles, they become arranged as membrane stacks, similar to the thylakoids of cyanobacteria Thylakoid membranes in the cytoplasm of cyanobacteria. Chloroplasts would be somewhat analogous to cyanobactria being present in the cytoplasm of algae and plant cells

  30. Photo-phosphorylation Is similar to electron transport in that: 1. a proton gradient is generated to provide PMF for ATP synthesis 2. it involves a series of membrane bound electron acceptors (known collectively as photosystems) 3. the membranes involved in photosynthesis contain an ATPase that is responsible for ATP synthesis when a proton gradient is established Is different in that: 1. it produces reduced cofactors in the form of NADPH 2. H2O is split into O2 to provide electrons and protons.

  31. Oxidative Photophosphorylation • Synopsis • Carbon dioxide (to be used in Carbon fixation) enters the outer and inner membranes • of the chloroplast or Cyanobacteria. • For the Calvin cycle, CO2 is fixed in the stroma of the chloroplast or the cytoplasm • of cyanobacteria • 3. Oxidative photophosphorylation occurs in the thylakoid membranes that are present • A. The photosystems and electron carriers are present in these membranes • 4. H20 is split into O2 inside the thylakoid space of thylakoids. • 5. Oxygen is released during oxidative photophosporylation and exits through the inner • and outer membranes of the chloroplasts/cyanobacteria • NADPH and ATP is released into the stroma of chloroplasts/cytoplasm of • cyanobacteria and used in CO2 fixation • 7. Chemiosmotic theory—shuttling of protons to produce the PMF required for ATP • synthesis. • A. During the transfer of electrons through the e- carriers in the thylakoid • membrane a proton gradient is achieved. • B. Protons are pumped into the thylakoid space during electron transfer • C. An ATP synthase complex is embedded in the thylakoid membrane • D. When the protons flow through the ATP synthase complex from the thylakoid • space into the stroma /cytoplasm—ATP is synthesized!!!!!

  32. Enlarged thylakoid in a chloroplast or in Cyanobacteria

  33. PhotosynthesisLight dependent reactions vs. Light independent reactions (Dark Reactions) Summary Rxn: 6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O OR 6CO2 + 6H2O  C6H12O6 + 6O2 chlorophyll Light reaction: Water + ADP + Pi + NADP Oxygen + ATP + NADPH light Dark reaction: Carbon dioxide + ATP + NADPH Glucose enzymes

  34. The Z pathway is used by the aerobic micro-organisms 1.algae 2. cyanobacteria. Oxidative phosphorylation involved 2 photosystems that require two separate photo absorption acts. 1. Photosystem I (PSI)Chlorophyll reaction center absorbs light at 700 nm 2. Photosystem II (PSII)Chlorophyll reaction center absorbs light at 680 nm

  35. The Z pathway allows the noncyclic flow of electrons seen in oxidative photophosphorylation • 1. ATP production • 2. NADP reduced to • NADPH for biosynthesis • Electrons/protons from • splitting water or exciting • photo reaction centers

  36. Step by step actions in noncyclic oxidative photo-phosphorylation • Chlorophyll Rxn center of PSII absorbs light at 680 nm • The chlorophyll Rxn center becomes energetically excited and loses • an electron (e-) • The e- is transferred through a series of membrane bound e- carriers • until the e- is transferred to the chlorophyll Rxn center of PSI • The transfer of e-s from the Rxn center of PSII to PSI creates a proton • gradient such that ATP is generated via chemiosmosis • Light excites the chlorophyll Rxn center of PSI such that an e- is • released from that Rxn center • 6. e-s are transferred through a series of membrane bound e- carriers in • PSI • The protons generated through this e- transfer is used to reduce NADP • to NADPH (NADPH is used in biosynthetic pathways) • The Rxn center of PSII meanwhile has lost an e- that must be replaced • This is accomplished when H2O is split to form O2 and protons. • The e-s are transferred thru membrane bound carriers to the Rxn center • Of PSII. This also generates PMF for ATP synthesis.

  37. Anaerobic Photosynthesis (cyclic) is used by the halophilic purple bacteria, the Heliobacteria and the Green sulfur bacteria. Only one photosystem is employed (PSI) The Rxn center of PSI absorbs light at 840 nm NADPH is usually not produced The bacteria get reducing power from other sources (external or internal) besides water

  38. Cyclic Anaerobic photo-phosphorylation H2S S2O3 H2S S2O3 • ATP production 2. In some cases NADP reduced to NADPH by reverse • electron flow 3. Reducing equivalents for biosynthesis can also come • from external sources besides water or from FeS centers within membranes.

  39. Step by step actions in cyclic anaerobic photo-phosphorylation • Light is absorbed by the Rxn center in PSI • e-s are transferred through membrane bound carriers to generate • PMF. • The excited e- is returned to the Rxn center of PSI • Where do the bacteria get the reducing equivalents for biosynthesis? • Purple bacteria: reverse e- flow through the membrane requires • ATP but can be used to reduce NADP to NADPH • Green Sulfur bacteria/Heliobacteria: FeS of the PSI can transfer • e-s and protons to molecules to be reduced (i.e. CO2) • Purple bacteria/Green sulfur bacteria: Sulfide in the form of H2S • or S2O3 serve as proton/electron donors that enter the chain at • cytochrome c2 for extra reducing power • (N.B. H2S or S2O3 are oxidized to elemental sulfur that can be stored in • bacteria or expelled)

More Related