Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download 1. anaerobic respiration 2. fermentation
Document related concepts
no text concepts found
Transcript
THE ANAEROBIC WAY OF LIFE : 1. ANAEROBIC RESPIRATION 2. FERMENTATION ANAEROB RESPIRATION Key Points Dissimilative 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 Alternative Electron Acceptors and the Redox Tower Anaerobic respiration other substances, such SO42- or NO3– is used as a terminal electron acceptor, instead of O2 Example 1. Nitrate reduction Figure 24.19 Nitrogen cycle 78% N2 Dissimulative NO3- reduction Denitrification by Pseudomonas stutzeri Denitrification by Pseudomonas stutzeri • Four terminal reductases – – – – Nap: Nitrate reductase (Mo-containing enzyme) Nir: Nitrite reductase Nor: Nitric oxide reductase N2or: Nitrous oxide reductase • All can function independently but they operate in unison Denitrification by Pseudomonas stutzeri • Electron donor: lactate, formate, H2, others – Uses special dehydrogenases for these. • Enzymes are membrane-bound • Periplasmic nitrate reductases (NapA) contains a molybdenum cofactor • Coupled to the generation of PMF • ATP synthesized by oxidative phosphorylation Nitrate vs. oxygen vs. denitrification respiration oxygen nitrite denitrification Example 2. Iron reduction FeIII-oxide Iron oxide reducing bacteria 2Fe(III) 2Fe(II) OM c-heme • Examples: – Geobacter, Shewanella, Rhodoferrax Q QH2 NADH2 NAD+ CM Example 3. Sulfate reduction Sulfate Reducing Bacteria • Vibrio • Gram negative • Has single polar flagellum • Mesophilic and pH optimal 7 • Has no endospore Electron transport and energy conservation in sulfate reducing bacteria Sulfate Reduction by Desulfovibrio vulgaris Sulfate reduction Acid Mine or Acid Rock Drainage acid sulfates heavy metals iron H+ Cu2+ SO42- Fe2+ 20 Acid Rock Drainage with Copper 21 How do Sulfate Reducing Bacteria Precipitate Metals? Biomineralization SO4 2- + organics HS- M2+[aq] + S2- biotic dissociation abiotic HS- + CO2 H+ + S2- MS[s] Fe0 as an Electron Donor for Sulfate Reduction indirect Fe2+ + H2 Fe0 SO42SRB direct Fe0 SO42- H2S SRB H2S Fe2+ 23 Fe0 as an Electron Donor for Sulfate Reduction indirect Reaction of Fe0 (Anoxic Corrosion) 8H+ + 4Fe0 4H2 + 4Fe2+ G’ = -20.1 kJ/4 mol Fe0 Reaction of Autotrophic Sulfate Reduction 2H+ + 4H2 + SO42- H2S + 4H2O G’ = -152.2 kJ/mol SO4224 Hypotheses: Benefits of Fe0 for Sulfate Reducing PRB Fe2+ formed attenuates excess sulfides SO42- reduced and removed, no discharge of sulfides FeS higher Ksp than heavy metal sulfides (Fe2+ doesn’t outcompete with precipitation of heavy metals) Oxidation of Fe0 forms high levels of alkalinity Can treat very acid drainage Additional metal removal mechanisms with hydroxides Long term source of electron donating equivalents 25 Direct abiotic reduction heavy metals by Fe0 Fe0 + Cu2+ abiotic Fe2+ + Cu0 26
Related documents