Download Methanogens and homoacetogens

Physiology and Diversity of Prokaryotes WS 2008/2009
2009/2019 (www.icbm.de/pmbio/)
Methanogens and
homoacetogens
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Examples for
anaerobic respirations
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Two types of carbon respiration
- Methanogenesis
- Homoacetogenesis
Low energy yield, but
…carbonate is almost
everywhere abundant.
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Alessandro Volta (1745-1827)
Lake Maggiore (Italy) November 3, 1776
Observation of “combustible air”
Physiology and Diversity of Prokaryotes WS 2009/2019 (www.icbm.de/pmbio/)
Methanogens
BROCK Microbiology: Chapter 13, 17
CYPIONKA Grundlagender Mikrobiologie: Chapter 15
Physiology and Diversity of Prokaryotes WS 2008/2009 (www.icbm.de/pmbio/)
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
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
The three domains of life
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Anaerobic degradation of organic matter
Complex polymers
(polysaccharides, lipids, proteins)
Hydrolysis
Monomers
(sugars, fatty acids, amino acids)
Fermentation
H2 + CO2
Formate
Short chain fatty acids and alcohols
(lactate, butyrate, propionate, ethanol)
Secondary fermentativ
bacteria
Acetate
Methanogenesis
CO2 + Methane
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
3 types for methanogenesis
Reaction
!G°´ (kJ/mol of methane)
Carbonate respiration
4 H2 + CO2 ! CH4 + 2 H2O
–135.6
4 Formate ! CH4 + 3 CO2 + 2 H2O
–130.1
4 2-Propanol + CO2 ! CH4 + 4 Acetone + 2 H2O
–36.5
2 Ethanol + CO2 ! CH4 + 2 Acetate
–116.3
C1-Compounds
Methanol + H2 ! CH4 + H2O
–112.5
4 Methanol ! 3 CH4 + CO2 + 2 H2O
–104.9
4 Methylamine + 2 H2O ! 3 CH4 + CO2 + 4 NH4
+
–75.0
2 Dimethylamine + 2 H2O ! 3 CH4 + CO + 2 NH4 +
4 Trimethylamine + 6 H2O ! 9 CH4 + 3 CO2 + 4 NH4
–73.2
+
2 Dimethylsulfide + 2 H2O ! 3 CH4 + CO2 + H2S
–74.3
–73.8
Acetoclastic
Acetate ! CH4 + CO2
–31.0
Physiology and Diversity of Prokaryotes WS 2006/2007
2009/2019 (www.icbm.de/pmbio/)
Oxidation state
Carbon dioxide (CO2)
+ IV
Reduction
8 electrons (e-)
Formyl (-COH)
Methylene (=CH2)
Methyl (-CH3)
Carbonate respiration
4 H2 + 1 CO2 ! CH4 + 2 H2O
- IV
Methan (CH4)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Anaerobic Respiration (i.g.: Methanogenesis)
Hydrogen + Carbon dioxide
Methan
H2 + CO2
CH4
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Anaerobic Respiration (i.g.: Methanogenesis)
Hydrogen + Carbon dioxide
Methan
H2 + CO2
CH4
Redox Balance
C +IV; H 0
C -IV; H 4(+I) 8 e-
4H2 + CO2
(e- donor) (e- acceptor)
CH4
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Anaerobic Respiration (i.g.: Methanogenesis)
Hydrogen + Carbon dioxide
Methane
H2 + CO2
CH4
Redox Balance
C +IV; H 0
C -IV; H 4(+I) 8 e-
4H2 + CO2
(e- donor) (e- acceptor)
CH4
Elemental Balance
8xH, 1xC, 2xO
4xH, 1xC
4H2 + CO2
CH4 + 2H2O
!G0 ’ = -50.75 + 2(-237.17) - (-394.4) = -130.7 kJ
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Carbonate respiration
4 H2 + CO2 ! CH4 + 2 H2O
Methanobacterium
Methanomicrobium
Methanospirillum
MF: Methanofuran
MP: Methanopterin
CoM: Coenzyme M
(Mercaptoethansulfonat)
F420: Factor F420
F430: Factor F430
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
F420-Fluorescence in Methanobacterium formicicum
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
C1-Reaction
e.g. Methanol
Methanolobus
Methanosarcina
4 methanol ! 3 CH4 + CO2 + 2 H2O
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Autofluorescence (F420) in Methanolobus sp.
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Aceticlastic (acetate)
Reaction
Methanosaeta
Methanosarcina
Acetate ! CH4 + CO2
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Methanophenazine
Electron
transport chain
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
acetate ! CH4 + CO2
!G0’ = -31.0 kJ/ mol acetate
acetate + SO42- ! 2 HCO3- + HS!G0’ = -47.6 kJ/ mol acetate
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Anaerobic degradation of organic matter
Complex polymers
(polysaccharides, lipids, proteins)
Hydrolysis
Monomers
(sugars, fatty acids, amino acids)
Fermentation
H2 + CO2
Formate
Short chain fatty acids and alcohols
(lactate, butyrate, propionate, ethanol)
Secondary fermentativ
bacteria
Acetate
Methanogenesis
CO2 + Methane
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Anaerobic Respiration (i.g.: Methanogenesis)
Hydrogen + Carbon dioxide
Methane
H2 + CO2
CH4
Redox Balance
C +IV; H 0
C -IV; H 4(+I) 8 e-
4H2 + CO2
(e- donor) (e- acceptor)
CH4
Elemental Balance
8xH, 1xC, 2xO
4xH, 1xC
4H2 + CO2
CH4 + 2H2O
!G0 ’ = -50.75 + 2(-237.17) - (-394.4) = -130.7 kJ
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Ethanol fermentation
Ethanol
C2H6O
Acetate + Hydrogen
C2H3O2- + H2
Ionic Balance
C2H6O
C2H3O2- + H2 + H+
Elemental Balance
C2H6O + H2O
C2H3O2- + 2H2 + H+
Redox Balance
C 2(-II); H 6(+I); O (-II)
C 2(0); H 3(+I); O 2(-II) + H (+I)
!G0 ’ = -369.41 + (-39.83) - [(-181.75) + (-237.17)] = 9.68 kJ
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Effect of hydrogen partial pressure
on free-energies
Ethanol fermentation:
ethanol + H2O
acetate + 2H2 + H+
[C]c [D]d
0
!G
RT
ln
!G =
+
[A]a [B]b
!G = !G0 + RT ln
[H2]2 [acetate] [H+ ]
[ethanol] [H2O]
at 10-4 atm H2
!G = !G0 + mRT ln [H2]
!G = 9.68 + 2RT ln [10-4 ] = -36.03 kJ/mol
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Syntrophic ethanol oxidation at
anaerobic conditions
!G0’ (kJ/reaction)
Ethanol fermentation
2 ethanol + 2H2O
+ 19.4
2 acetate + 4H2 + 2H+
Methanogenesis
4H2 + CO2
- 130.7
CH4 + 2H2O
Syntrophic coupled reaction
2 ethanol + CO2
2 acetate + CH4 + 2H+
- 111.3
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Syntrophic co-culture “Methanobacillus omelianskii”
ethanol
CO2
Interspecies Hydrogen-transfer
H2
H2
CH4
acetate
Strain S
Strain MoH
“Methanobacillus omelianskii”
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Syntrophic co-cultures
Interspecies hydrogen transfer
Hydrogen-producer
Hydrogen-consumer
Fermentation
fatty-acids
(e.g., butyrate, propionate)
alcohols
(e.g.,ethanol)
Anaerobic Respiration
CO2, SO4-2, NO3-
H2
H2
acetate + CO2
acetate, methane, HS-, N2O,
NO, N2
Syntrophomonas
Syntrophobacter
Methanogens
Sulfate-reducing bacteria
Denitrifyers
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Vertical profile of potential electron
acceptors in marine sediments
Eo’ [mV]
O2
NO3MnO2
Fe(III)
SO42-
CH4
O2/H2O +820
NO3-/N2 +751
NO3-/NH4+ +363
MnO2/Mn2++390
Aerobic respiration
Denitrification
Nitrate ammonification
Manganese reduction
FeOOH +150
SO42-/HS- -218
So/HS-240
CO2/CH4 -244
Iron reduction
Sulfate reduction
Sulfur reduktion
Methanogenesis
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Profile of sulfate and methane in an intertidal flat sediment
(German Wadden Sea)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Sulfate-methane
transition zone
Profile of sulfate and methane in an intertidal flat sediment
(German Wadden Sea)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
16S rRNA target Fluorescence
in situ hybridization
Orphan et al. (PNAS 2002)
Boetius et al. (nature 2000)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Anaerobe Oxidation von Methan
Proposed reaction:
CH4 + SO2-4 ! HCO- 3 + HS- + H2O (!G0’ = -25.0 kJ/ mol methane)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
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 O2, NO3–, Fe3+ and SO42– are limiting.
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Global methane emission from different habitats
Animals (rumen)
Termites
Rice fields
Ocean & lakes
in millionT/year
80-100
25-150
70-120
1-20
Biogenic
Abiogenic
300-820
48-155
Physiology and Diversity of Prokaryotes WS 2006/2007
2009/2019 (www.icbm.de/pmbio/)
Homoacetogens
BROCK Microbiology: Chapter 17
CYPIONKA Grundlagender Mikrobiologie: Chapter 15
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Complex polymers
(polysaccharides, lipids, proteins)
Hydrolysis
Monomers
(sugars, fatty acids, amino acids)
Fermentation
H2 + CO2
Formate
Short chain fatty acids and alcohols
(lactate, butyrate, propionate, ethanol)
Acetate
Homoacetogenesis
Physiology and Diversity of Prokaryotes WS 2006/2007
2009/2019 (www.icbm.de/pmbio/)
Oxidation state
+ IV
Carbon dioxide (CO2)
Reduction
4 electrons (e-)
Carbonate respiration
4 H2 + 2 CO2 ! CH3COO- + H+ + 2 H2O
Aver. 0
Acetate
(CH3COO-)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
The acetyl-CoA pathway
Moorella
thermoaceticum
Acetyl-CoA- or
Wood-Ljungdahl
Pathway
H2 Electrondonor
CO2 Electronenacceptor
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
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)
CO2 + H2 ! CO + H2O
- The CO2 reduction must be considered as bifunctional
pathway: A) energy metabolism B) C-fixation for
biosynthesis
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
Homoacetogenic bacteria
- Extremely heterogenous group of strict anaerobes with
the ability to reduce CO2 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)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
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
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)
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)
Physiology and Diversity of Prokaryotes WS 2009/2010 (www.icbm.de/pmbio/)