Methanogens and homoacetogens

Transcription

1 Physiology and Diversity of Prokaryotes WS 2009/ /2009 ( Methanogens and homoacetogens Examples for anaerobic respirations

2 Two types of carbon respiration - Methanogenesis - Homoacetogenesis Low energy yield, but carbonate is almost everywhere abundant. Alessandro Volta ( ) Lake Maggiore (Italy) November 3, 1776 Observation of combustible air

3 Physiology and Diversity of Prokaryotes WS 2009/2019 ( Methanogens BROCK Microbiology: Chapter 13, 17 CYPIONKA Grundlagender Mikrobiologie: Chapter 15 Physiology and Diversity of Prokaryotes WS 2008/2009 ( Methanogens represent a large group of microorganisms which share three features: Formation of methane as the major product of their energy metabolism They are strict anaerobes They are members of the domain Archaea

4 The three domains of life

5 Anaerobic degradation of organic matter Hydrolysis Fermentation Complex polymers (polysaccharides, lipids, proteins) Monomers (sugars, fatty acids, amino acids) Short chain fatty acids and alcohols (lactate, butyrate, propionate, ethanol) H 2 + CO 2 Formate Secondary fermentativ bacteria Acetate Methanogenesis CO 2 + Methane

6 3 types for methanogenesis Reaction!G (kj/mol of methane) Carbonate respiration 4 H 2 + CO 2! CH H 2 O Formate! CH4 + 3 CO H 2 O Propanol + CO 2! CH4 + 4 Acetone + 2 H2O Ethanol + CO 2! CH Acetate C1-Compounds Methanol + H 2! CH 4 + H 2 O Methanol! 3 CH 4 + CO H 2 O Methylamine + 2 H 2 O! 3 CH 4 + CO NH Dimethylamine + 2 H 2 O! 3 CH 4 + CO + 2 NH Trimethylamine + 6 H 2 O! 9 CH CO NH Dimethylsulfide + 2 H 2 O! 3 CH 4 + CO 2 + H 2 S 73.8 Acetoclastic Acetate! CH 4 + CO Physiology and Diversity of Prokaryotes WS 2009/ /2007 ( Carbon dioxide (CO 2 ) Oxidation state + IV Reduction 8 electrons (e - ) Formyl (-COH) Methylene (=CH 2 ) Methyl (-CH 3 ) Carbonate respiration 4 H CO 2! CH H 2 O - IV Methan (CH 4 )

7 Anaerobic Respiration (i.g.: Methanogenesis) Hydrogen + Carbon dioxide Methan H 2 + CO 2 CH 4 Anaerobic Respiration (i.g.: Methanogenesis) Hydrogen + Carbon dioxide Methan H 2 + CO 2 CH 4 Redox Balance C +IV; H 0 C -IV; H 4(+I) 8 e - 4H 2 + CO 2 CH 4 (e - donor) (e - acceptor)

8 Anaerobic Respiration (i.g.: Methanogenesis) Hydrogen + Carbon dioxide Methane H 2 + CO 2 CH 4 Redox Balance C +IV; H 0 C -IV; H 4(+I) 8 e - 4H 2 + CO 2 CH 4 (e - donor) (e - acceptor) Elemental Balance 8xH, 1xC, 2xO 4H 2 + CO 2 4xH, 1xC CH 4 + 2H 2 O!G 0 = ( ) - (-394.4) = kj Carbonate respiration 4 H 2 + CO 2! CH H 2 O Methanobacterium Methanomicrobium Methanospirillum MF: Methanofuran MP: Methanopterin CoM: Coenzyme M (Mercaptoethansulfonat) F420: Factor F420 F430: Factor F430

9 F420-Fluorescence in Methanobacterium formicicum C1-Reaction e.g. Methanol Methanolobus Methanosarcina 4 methanol! 3 CH 4 + CO H 2 O

10 Autofluorescence (F420) in Methanolobus sp. Aceticlastic (acetate) Reaction Methanosaeta Methanosarcina Acetate! CH 4 + CO 2

11 Methanophenazine Electron transport chain acetate! CH 4 + CO 2!G 0 = kj/ mol acetate acetate + SO 4 2-! 2 HCO HS -!G 0 = kj/ mol acetate

12 Anaerobic degradation of organic matter Hydrolysis Fermentation Complex polymers (polysaccharides, lipids, proteins) Monomers (sugars, fatty acids, amino acids) Short chain fatty acids and alcohols (lactate, butyrate, propionate, ethanol) H 2 + CO 2 Formate Secondary fermentativ bacteria Acetate Methanogenesis CO 2 + Methane Anaerobic Respiration (i.g.: Methanogenesis) Hydrogen + Carbon dioxide Methane H 2 + CO 2 CH 4 Redox Balance C +IV; H 0 C -IV; H 4(+I) 8 e - 4H 2 + CO 2 CH 4 (e - donor) (e - acceptor) Elemental Balance 8xH, 1xC, 2xO 4H 2 + CO 2 4xH, 1xC CH 4 + 2H 2 O!G 0 = ( ) - (-394.4) = kj

13 Ethanol fermentation Ethanol Acetate + Hydrogen C 2 H 6 O C 2 H 3 O H 2 Ionic Balance C 2 H 6 O C 2 H 3 O H 2 + H + Elemental Balance C 2 H 6 O + H 2 O C 2 H 3 O H 2 + H + Redox Balance C 2(-II); H 6(+I); O (-II) C 2(0); H 3(+I); O 2(-II) + H (+I)!G 0 = (-39.83) - [( ) + ( )] = 9.68 kj Effect of hydrogen partial pressure on free-energies Ethanol fermentation: ethanol + H 2 O acetate + 2H 2 + H +!G =!G 0 + RT ln [C]c [D] d [A] a [B] b!g =!G 0 + RT ln [H 2 ]2 [acetate] [H + ] [ethanol] [H 2 O] at 10-4 atm H 2!G =!G 0 + mrt ln [H 2 ]!G = RT ln [10-4 ] = kj/mol

14 Syntrophic ethanol oxidation at anaerobic conditions Ethanol fermentation 2 ethanol + 2H 2 O 2 acetate + 4H 2 + 2H +!G 0 (kj/reaction) Methanogenesis 4H 2 + CO 2 CH 4 + 2H 2 O Syntrophic coupled reaction 2 ethanol + CO 2 2 acetate + CH 4 + 2H Syntrophic co-culture Methanobacillus omelianskii ethanol CO 2 Interspecies Hydrogen-transfer H 2 H 2 CH 4 acetate Strain S Strain MoH Methanobacillus omelianskii

15 Syntrophic co-cultures Interspecies hydrogen transfer Hydrogen-producer Hydrogen-consumer Fermentation Anaerobic Respiration fatty-acids CO 2, SO -2 4, NO - 3 (e.g., butyrate, propionate) alcohols (e.g.,ethanol) H 2 H 2 acetate + CO 2 acetate, methane, HS -, N 2 O, NO, N 2 Syntrophomonas Syntrophobacter Methanogens Sulfate-reducing bacteria Denitrifyers 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

16 Profile of sulfate and methane in an intertidal flat sediment (German Wadden Sea) Sulfate-methane transition zone Profile of sulfate and methane in an intertidal flat sediment (German Wadden Sea)

17 16S rrna target Fluorescence in situ hybridization Orphan et al. (PNAS 2002) Boetius et al. (nature 2000) Anaerobe Oxidation von Methan Proposed reaction: CH 4 + SO 2-4! HCO HS - + H 2 O (!G 0 = kj/ mol methane)

18 Habitats of Methanogens - Anoxic sediments: marsh, swamp,lake sediments etc. - Animal digestion tracts: rumen, large intestine of monagastric animals (such as humans, swine, and dogs) - Geothermal sources, hydrothermal vents - Artifical biodegradation facilities: sewage sludge - Endosymbionts of various anaerobic protozoa Methanogenic archaea are abundant in habitats where electron acceptors such as O 2, NO 3, Fe 3+ and SO 4 2 are limiting. Global methane emission from different habitats in milliont/year Animals (rumen) Termites Rice fields Ocean & lakes 1-20 Biogenic Abiogenic

19 Physiology and Diversity of Prokaryotes WS 2009/ /2007 ( Homoacetogens BROCK Microbiology: Chapter 17 CYPIONKA Grundlagender Mikrobiologie: Chapter 15 Hydrolysis Fermentation Complex polymers (polysaccharides, lipids, proteins) Monomers (sugars, fatty acids, amino acids) Short chain fatty acids and alcohols (lactate, butyrate, propionate, ethanol) H 2 + CO 2 Formate Acetate Homoacetogenesis

20 Physiology and Diversity of Prokaryotes WS 2009/ /2007 ( Carbon dioxide (CO 2 ) Oxidation state + IV Reduction 4 electrons (e - ) Carbonate respiration 4 H CO 2! CH 3 COO - + H H 2 O Aver. 0 Acetate (CH 3 COO - ) Moorella thermoaceticum The acetyl-coa pathway Acetyl-CoA- or Wood-Ljungdahl Pathway H 2 Electrondonor CO 2 Electronenacceptor

21 The acetyl-coa pathway - In contrast to other carbon fixation pathways, not a cycle - two linear reaction series resulting in A) a methyl- and B) a carbonyl group - key enzyme: CO-DH (Carbon monooxide dehydrogenase/acetyl-coa synthase) CO 2 + H 2! CO + H 2 O - The CO 2 reduction must be considered as bifunctional pathway: A) energy metabolism B) C-fixation for biosynthesis

22 Homoacetogenic bacteria - Extremely heterogenous group of strict anaerobes with the ability to reduce CO 2 to acetate for generation of energy - The key enzyme is the carbonmonoxide dehydrogenase - Higher efficiency compared to fermentation (both acetyl-coa derived from pyruvate can be used for energy conservation) - Electron donor: hydrogen and a variety of organic compounds (sugars, amino acids, carbonic acids) - Acetate is major end product (in contrast to other acetogenic organisms) Habitats of homoacetogenic bacteria Due to their diversity with respect to the substrate spectrum homoacetogenic bacteria are abundant in almost all nonmarine environments: - freshwater sediments - sewage sludge - rumen of cow, cheep etc. - biofilms

23 Organisms using the acetyl-coa pathway I. For energy metabolism (homoacetogenic bacteria) Acetobacterium, Clostridium, Desulfotomaculum, Eubacterium, Treponema II. For carbon dioxide fixation Autotrophic homoacetogenes, methanogenes, SRB III. Acetate oxidation for energy metabolism Complete-oxidizing SRB (w/o Desulfobacter), acetoclastic methanogens (Methanosaeta, Methanosarcina)