Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Microbial Metabolism glycolysis Kreb`s cycle (TCA or citric acid cycle
Document related concepts
Transcript
Microbial Metabolism— Procuring Energy! Metabolic diversity Energy flow For Energy For Energy Carbon Flow for Anabolism Key Points Dissimulative metabolism—Reduction of chemicals for energy—much material must be used to achieve sufficient energy for growth Assimilative metabolism—Reduction of chemicals for biomass—the cell only uses as much starting material as required 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 In anaerobic metabolism Nitrate or I Sulfate serve as terminal FADH electron Co Q II FAD acceptors at the end of the III electron Thus under anaerobic transport conditions some organisms can still obtain high levels of energy chain NADHNAD IV NO3- N2 SO4-- H2S Mixotrophs, Energy from oxidation of organic chemicals inorganic chemicals are reduced. Denitrification (Nitrate reduction) Some Pseudomonas, Bacillus and Thiobacillus spp. Nitrate reduction is mediated by enzymes 1. nitrate reductase (NR) 2. nitric oxide reductase (NcOR) 3. nitrous oxide reductase (NsOR) NR NR NcOR NsOR NO3- NO2- NO N2O N2 Gases to atmosphere 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) 2. 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. 3. 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 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) NR NR NcOR NsOR NO3- NO2- NO N2O N2 Gases to atmosphere Significance of denitrification 2. 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. NR NR NcOR NsOR NO3- NO2- NO N2O N2 NO2sunlight NR N2O NO ozone H2O NO2 - Acid rain 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) 2. 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. 3. 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 Sulfate Reduction Bacteria responsible for this are widespread in aquatic environments Sulfate reduction is mediated by enzymes 1. ATP sulfurylase (ATPS) 2. APS reductase (APSR) 3. sulfite reductase (SR) ATPS APSR SR --SO4 SO3 H2S Excreted into environment 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!!!) Carbon dioxide reduction Methanogenesis (methanogens: anaerobic archaebacteria) 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 Glycolysis pyruvate FERMENTATION Formate, Acetate Lactate, Proprionate Butyrate, etc Membrane associated reactions of methanogenesis CH4 excreted CO2 and protons (H2) 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) Anoxic digestion of sludge 1. Methanogens use protons from catabolism and fermentation to reduce CO2 from fermentation to methane. 2. The methane is collected as natural gas to fuel and heat the sewage plant or burned off. 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 glucoseglycolysis 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!!! Stop here Chemolithotrophy—obtaining energy from inorganic chemicals 1. inorganic chemicals are oxidized as coenzymes in the electron transport chain are reduced. 2. Oxygen serves as the terminal electron acceptor in electron transport 3. 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 chemolithotropy 4. 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 X NADHNAD Chemolithotrophy Co Q O2 H2 O X FADH FAD Fe2+ Fe3+ NH4 NO2- /NO3H2S/S2O32- H2SO4 Sulfur and Iron oxidation (Thiobacillus thiooxidans, Thiobacillus ferrooxidans and others.) 1. Fe2+ Fe3+ ferrous iron to ferric iron 2. H2S elemental sulfurH2SO4 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 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 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 1. Bacteria live in the GI tract of tube worms/ the gills of mussels and clams. 2. Tube worms/mussels/clams provide CO2 as a carbon source for the bacteria. 3. 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 Significance of sulfur and iron oxidation Pollution/Acid mine Drainage (Thiobacillus and Metallogenium spp.) 1. 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) 6. Acid soon kills the aquatic life at the bottom of stream bed 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 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. Nitrification/Nitrogen oxidation by nitrifying bacteria A two step process mediated by two genera of bacteria NH4 NO2Nitrosomonas spp. ammonium to nitrite NO2- NO3Nitrobacter 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 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 Oxidative and Anaerobic Photophosphorylation (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 Photosynthetic membranes of the bacteria Thylakoid membranes in the cytoplasm of cyanobacteria. Chloroplasts would be somewhat analogous to cyanobactria being present in the cytoplasm of algae and plant cells 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 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. Oxidative Photophosphorylation Synopsis 1. Carbon dioxide (to be used in Carbon fixation) enters the outer and inner membranes of the chloroplast or Cyanobacteria. 2. 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 6. 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!!!!! Enlarged thylakoid in a chloroplast or in Cyanobacteria Photosynthesis Light dependent reactions vs. Light independent reactions (Dark Reactions) Summary Rxn: OR 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O 6CO2 + 6H2O C6H12O6 + 6O2 chlorophyll Light reaction: Water + ADP + Pi + NADP Oxygen + ATP + NADPH light Dark reaction: Carbon dioxide + ATP + NADPH Glucose enzymes 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 The Z pathway allows the noncyclic flow of electrons seen in oxidative photophosphorylation 1. ATP production 2. NADP reduced to NADPH for biosynthesis 3. Electrons/protons from splitting water or exciting photo reaction centers Step by step actions in noncyclic oxidative photo-phosphorylation 1. Chlorophyll Rxn center of PSII absorbs light at 680 nm 2. The chlorophyll Rxn center becomes energetically excited and loses an electron (e-) 3. The e- is transferred through a series of membrane bound e- carriers until the e- is transferred to the chlorophyll Rxn center of PSI 4. The transfer of e-s from the Rxn center of PSII to PSI creates a proton gradient such that ATP is generated via chemiosmosis 5. 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 7. The protons generated through this e- transfer is used to reduce NADP to NADPH (NADPH is used in biosynthetic pathways) 8. The Rxn center of PSII meanwhile has lost an e- that must be replaced 9. This is accomplished when H2O is split to form O2 and protons. 10. The e-s are transferred thru membrane bound carriers to the Rxn center Of PSII. This also generates PMF for ATP synthesis. 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 Cyclic Anaerobic photo-phosphorylation H2 S S2O3 H2 S S2 O 3 1. 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. Step by step actions in cyclic anaerobic photo-phosphorylation 1. Light is absorbed by the Rxn center in PSI 2. e-s are transferred through membrane bound carriers to generate PMF. 3. The excited e- is returned to the Rxn center of PSI Where do the bacteria get the reducing equivalents for biosynthesis? 1. Purple bacteria: reverse e- flow through the membrane requires ATP but can be used to reduce NADP to NADPH 2. Green Sulfur bacteria/Heliobacteria: FeS of the PSI can transfer e-s and protons to molecules to be reduced (i.e. CO2) 3. 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)
