Physiological diversity

Transcription

1 Physiological diversity Principles Energetic considerations Biochemical pathways Organisms Ecological relevance Physiological diversity Sulfate- and nitrate reducers (5. Nov.) Methanogens and homoacetogens (10. Nov.) Chemolithotrophs (11. Nov.) Photosynthesis (12. Nov.) Recapitulation (13. Nov.) Written test II (16. Nov.)

2 Sulfate and nitrate reducers Martin Könneke Recommended text books

3 Aerobic respiration vs fermentation NADH Glycolysis Pyruvic acid ATP NADH Acetyl CoA Pyruvic acid NADH ATP TCA (Krebs) cylce Formation of fermentation end products NADH CO 2 Substrate level phosphorilation Electrons ATP Electron transport chain and chemiosmosis Aerobic respiration Chemiosmosis

4 Fermentation Substrate-level phosphorylation Organic compounds Fermentation product NAD + Energy-rich compounds NADH Oxidized compound ADP ATP Hydrolysis Complex polymers (polysaccharides, lipids, proteins) Fermentation Monomers (sugars, fatty acids, amino acids) Short chain fatty acids and alcohols (lactate, butyrate, propionate, ethanol) H 2 + CO 2 Formate Acetate?????????

5 Anaerobic respiration Utilization of terminal electron acceptors others than oxygen Electron transport systems analog to aerobes (cytochromes, quinones, iron-sulfur and other proteins) Strict anaerobes (sulfate reducers + nitrate reducers) Facultative anaerobes (nitrate reducers) Anaerobic respiration Electron-donating reaction Membrane associated electron transport Terminal electronaccepting reaction Reduced organic and Inorganic compounds Proton motive force Oxidized compounds others than O 2 Generation of ATP Less energy than aerobic respiration, but usually more than fermentation!

6 Hydrolysis Complex polymers (polysaccharides, lipids, proteins) Fermentation Monomers (sugars, fatty acids, amino acids) Short chain fatty acids and alcohols (lactate, butyrate, propionate, ethanol) H 2 + CO 2 Formate Acetate CO 2 + Sulfide CO 2 + Methane CO 2 + NH 4 /N 2 Examples for anaerobic respirations

7 Dissimilatory nitrate reducers Brock Biology of Microorganisms: Chapter 12, 17, 18 The biological nitrogen cycle Nitrate reduction NO 3 - NO 2 - Denitrification NO N 2 O Nitrite Ammonification DNRA Nitrification N 2 Anammox NH 2 OH Nitrogen fixation NH 4 +

8 The biological nitrogen cycle Nitrate reduction NO 3 - Denitrification NO N 2 O NO 2 - Nitrite ammonification N 2 NH 4 + Denitrification - Reduction of nitrate to nitrogen Anaerobic respiration with anorganic nitrate as electron acceptor Formation of gaseous compounds nitrous oxide (N 2 O), nitric oxide (NO) und nitrogen (N 2 ) Results in a loss of nitrogen in the environment (agriculture - wastewater treatment) Initial step is catalyzed by the nitrate reductase Many facultative anaerobic prokaryotes are denitrifiers

9 Oxidation state Nitrate (NO 3- ) + V Reduction 5 electrons (e - ) Nitrite (+III) Nitric oxide (+II) Nitrous oxide (av. +I) Denitrification 2NO e H +! N 2 + 6H 2 O 0 Nitrogen (N 2 )

10 Denitrification in Pseudomonas stutzeri Oxygen- and nitrate respiration in E. coli

11 Haloferax denitrificans (facultatic aerobe) Ferroglobus placidus (strict anaerobe) Widespread among the Bacteria Oxidation state Nitrate (NO 3- ) + V 2 electrons (e - ) Nitrite (+III) 6 electrons (e - ) Nitrate ammonification - III Ammonia (NH 3 )

12 Nitrate ammonification - Reduction of nitrate to ammonia Anaerobic respiration with inorganic nitrate as electron acceptor (energy yielding step) Temporary accumulation of nitrite Reduction of nitrite to ammonia is an exergonic reaction (kind of fermentation process) Removal of reduction equivalents Common in facultative anaerobes (Enterobacter, E. coli) and strict anaerobes (Ammonifex, Wolinella, certain sulfate reducers)

13 Examples for anaerobic respirations

14 Relation of free energy to reduction potential!g 0 = - nf! E 0 n F = Number of electrons = Faraday s constant (96.48 kj/v)! E 0 = Difference in potentials of half-reactions = E 0 electron-accepting - E 0 electron-donating Vertical profile of potential electron acceptors in marine sediments O 2 NO 3 - MnO 2 Fe(III) SO 4 2- E o [mv] O 2 /H 2 O +820 Aerobic respiration NO 3- /N Denitrification NO 3- /NH Nitrate ammonification MnO 2 /Mn Manganese reduction FeOOH +150 Iron reduction SO 2-4 /HS Sulfate reduction S o /HS Sulfur reduktion CO 2 /CH Methanogenesis CH 4

15 Hydrolysis Complex polymers (polysaccharides, lipids, proteins) Fermentation Monomers (sugars, fatty acids, amino acids) Short chain fatty acids and alcohols (lactate, butyrate, propionate, ethanol) H 2 + CO 2 Formate Acetate CO 2 + Sulfide CO 2 + Methane CO 2 + NH 4 /N 2 Hydrolysis Complex polymers (polysaccharides, lipids, proteins) Fermentation Monomers (sugars, fatty acids, amino acids) Short chain fatty acids and alcohols (lactate, butyrate, propionate, ethanol) H 2 + CO 2 Formate Acetate CO 2 + Sulfide Sulfidogenesis (Dissimilatory sulfate reduction)

16 Dissimilatory sulfate reducers Heterogenous group of prokaryotes that gain energy by the reduction of sulfate to sulfide SO e -! S 2- Brock Biology of Microorganisms: Chapter 12, 17, 18 Sulfate-reducing prokaryotes Sulfate-reducing prokaryotes (Desulfo-) (in contrast to sulfur-reducing prokaryotes (Desulfuro-)) 1864 H 2 S is product of a biological process (Meyer) 1886 anaerobic degradation of cellulose with gypsum (CaSO 4 ) (Hoppe-Seyler) 1895 first isolate (Bejerinck) 1953 detection of cytochrom (Postgate) 1980 complete oxidization of acetate (Widdel)

17 Oxidation state Sulfate (SO 4- ) + VI Reduction 8 electrons (e - ) Sulfite (+IV) Thiosulfate (av. +II) Sulfur (0) - II Hydrogen sulfide (H 2 S) Biochemical pathway Uptake of sulfate Activation of sulfate Sulfate reduction Generation of proton motive force Release of sulfide

18 Activation of sulfate ATP sulfurylase APS kinase

19 Activation of sulfate on the expense of energy (ATP) Dissimilatory sulfite reductase Dsr A specific biomarker for SRB!

20 Lateral gene transfer of dsrab genes 16S rrna DsrAB delta proteobacteria LGC Klein et al., (2001) J Bac 183(20): Incomplete oxidation of lactate 1 "m Desulfovibrio desulfuricans Incomplete oxidation of lactate (e.g. Desulfovibrio spec.) 2 CH 2 CHOHCOO - + SO 4 2-! 2 CH 3 COO HCO HS - + H +!G 0 = -160 kj/ mol sulfate

21 Electron transport and energy conservation in incomplete-oxidizing Sulfate-reducing bacteria (SRB) Oxidation of acetate CH 3 COO - + SO 4 2-! 2 HCO HS - Electron accepting reaction SO H +! HS - Electron donating reaction CH 3 COO -! 2 HCO H + 10 "m Desulfobacter postgatei

22 Oxidation of acetate CH 3 COO - + SO 4 2-! 2 HCO HS - Electron accepting reaction SO H +! HS - + VI - II Electron donating reaction CH 3 COO -! 2 HCO H + Aver. 0 + IV Complete oxidation of acetate CH 3 COO - + SO 4 2-! 2 HCO HS - Electron accepting reaction SO e - + H +! HS - + VI - II Electron donating reaction CH 3 COO -! 2 HCO e - + H + Aver. 0 + IV E V V!G 0 = - nf! E 0

23 Complete oxidation of acetate (e.g. Desulfobacter spec.) CH 3 COO - + SO 2-4! 2 HCO HS -!G 0 = kj/ mol sulfate Complete oxidation of lactate (e.g. Desulfosarcina spec.) 2 CH 2 CHOHCOO - +3 SO 4 2-! 6 HCO HS - + H +!G 0 = -85 kj/ mol sulfate!g 0 = -127 kj/ mol lactate Incomplete oxidation of lactate (e.g. Desulfovibrio spec.) 2 CH 2 CHOHCOO - + SO 2-4! 2 CH 3 COO HCO HS - + H +!G 0 = -160 kj/ mol sulfate!g 0 = -80 kj/ mol lactate Electron-donors Hydrogen, fatty acids, alkenes, aromatic compounds sugars,amino acids, alcohols Alternative electron acceptors sulfur, thiosulfate, sulfite nitrate, iron, uranium Fermentation Sulfur Disproportionation (S 2 O H 2 O! SO H 2 S) Autotrophic growth A) Reverse tricarboxylic cycle (Desulfobacter spp.) B) Acetyl-CoA pathway

24 Desulfovibrio desulfuricans Desulfonema limicola Desulfobulbus propionius Desulfobacter postgatei Desulfosarcina variabilis Desulfuromonas acetoxidans

25 Hyperthermophilic sulfate-reducing archaea

26 Habitats of sulfate-reducing bacteria Almost in all anoxic environment where sulfate is available A) Marine sediments B) Freshwater sediments C) Biofilms and microbial mats D) Anaerobic sewage sludge E) Related to human diseases F) Geothermal sources Temperature range: - 1.8ºC to 105ºC