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 Methanogens Manish Patel. What are they?  Taxonomy  Classified as archaebacteria  Over 50 species, in 5 orders and 9 families  Typically appear.

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Presentation on theme: " Methanogens Manish Patel. What are they?  Taxonomy  Classified as archaebacteria  Over 50 species, in 5 orders and 9 families  Typically appear."— Presentation transcript:

1  Methanogens Manish Patel

2 What are they?  Taxonomy  Classified as archaebacteria  Over 50 species, in 5 orders and 9 families  Typically appear coccoid or bacilli  Some have cell wall made of pseudopeptidoglycan or a layer of proteins  Obligate Anaerobes – O 2 is poisonous

3 Where are they on Earth?  Found in environments depleted of electron acceptors (O 2, NO 3, Fe 3+, SO 4 ):  Swamps and marshes  Largest natural methane source – 250 Tg  Sediments at the bottom of rivers and lakes/oceans  Digestive tracts of animals  Cattle livestock by humans - ~150 Tg  Extremophiles  Geothermal environments  Found in ice cores from 3 km below Greenland and 4-5 km below the surface in South African Gold Mines  Found in sediments from “White Smoker” chimneys, 2600m deep in the East Pacific Rise (Temp: 48-95˚C; Pressure: 200 atm)  Can reproduce in temperatures ranges of ˚C

4 How do they survive?  Methanogenesis:  Formation of methane by microbes.  Use carbon dioxide, formate, methanol, methylamines, methylthiols and acetate for carbon source.  H 2 is their electron source.  Not to be confused with methano trophs

5 General Overview for CO 2 

6 Actual ∆G’ is ~ +40kJ/mol because of low H 2 (electron source) partial pressure. Catalyzed by formylmethanofuran dehydrogenase Reduction driven by transmembrane electrochemical Na + potential

7 Formyl transfer catalyzed by formyl transferase Tetrahydromethanopterin (H 4 MPT) is analogous to tetrahydrofuran (H 4 F) as a methyl- carrier Reversible hydrolysis of N 5,N l0 -methenyl- H 4 MPT to N 5 -formyl-H 4 MPT, is catalyzed by N 5,N 10 -methenyl-H 4 MPT cyclohydrolase

8 Catalyzed by methylene H 4 MPT dehydrogenase twice. Utilizes a reduced coenzyme F 420, a deazaflavine derivative and hydride acceptor (from H 2 ). Alternative enzymes use H 2 directly. F 420 is unique to methanogens.

9 F 420 H 2 is regenerated by an F 420 -dependent hydrogenase. All of these F 420 -dependent hydrogenases contain flavin, Ni, and Fe-S clusters.

10 Catalyzed by a transmembrane methyltransferase, which also acts as a sodium ion pump. Na + gradient could be used as mentioned before in MF formation or in a Na + -driven ATP synthase. Coenzyme M is also exclusive to methanogenic microbes.

11 Catalyzed by methyl-coenzyme M reductase Utilizes 2 coenzymes: 7-mercaptoheptanoylthreonine phosphate (HS-HTP) reduces Coenzyme M and displaces methane F 430, a nickel porphinoid, coordinates the displacement.

12 A F 420 -nonreactive hydrogenase activates H 2 and channels the electrons into the electron transport chain, and the electrons are transferred to CoM-S-S-HTE In some methanogens, this is coupled with a Na + pump instead of a H + pump. In one species, this complex contains nickel, FAD, non-heme iron, and acid-labile sulfur. Also, b -type cytochromes are present for use in an electron transport chain.

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14 Alternative Carbon Sources

15 How does Methanogenesis play into the whole metabolism?

16 We know how they work. How can we find them in space?

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19 Not what we imagined.

20 Looking for Methanogens  When looking for potential extraterrestrial methanogenic life, the presence of methane alone does not indicate life.  Considering the flux of methane helps to determine whether methane biogenic or abiogenic.  Focus on atmospheric methane at the surface.  The observed non-uniformity in methane could be due to localized microbial colonies or localized hydrogeochemical sources.  Also determine whether to look for past life or current life. One factor could be where liquid water was or is currently.

21 Methane Sources and Sinks  Methane on Mars could be produced from any one of the four potential sources:  1. Internal, such as volcanoes or hydrothermal sources  2. Exogenous, such as meteorites, comets, or interplanetary dust particles.  3. Internal, such as a hydrogeochemical process involving serpentinization.  4. Biological. On Earth:

22 Methane Sources and Sinks  Loss of methane on Mars  Primarily from photolysis, giving Mars’ methane a photochemical lifetime of about 300 years.  Reacting with other trace chemcials/oxidants (peroxide)  Diffusion into the regiolith  Significant sinks could be responsible for non-uniform CH 4 distribution.

23 Summing Up Methane Flux

24  Spectroscopic studies  Taking into account doppler shifts and to find CH 4 signatures  Fourier Transform Spectrometer at the Canada–France–Hawaii Telescope  Infrared Telescop Facility (IRTF)  Gemini Telescope  Robots  Take soil samples for spectroscopy Techniques

25 Life Tests:  Carbon Isotopes:  Less energy to form a bond between 12 C and 12 C elements than between 12 C and 13 C elements.  It is a good indicator of life, as we know it on Earth.  PDB (Pee Dee Belemnite) Inorganic Standard value, R std = 13 C/ 12 C =  Requires a measureable quantity in the atmosphere. Mars requires instruments capable of measuring 0.01ppbv

26 Life Tests:  Chirality  Organic molecules are mostly left-handed on Earth, but amino acids from meteorites have been found to also be left-handed.  Overtime, organic molecules will tend to form a racemic mixture, so the presence of chiral organic molecules could indicate present life.  Fluorescence  F 420 detected with excitation-emission wavelengths of nm  Potential test if core samples can be obtained from deep enough, where methanogens would reside, past the permafrost.

27 References:  Blaut, M. “Metabolism of Methanogens” Antonie van Leeuwenhoek  Thauer, R. K. “Biochemistry of Methanogenesis” Microbiology  Atreya, S. K.; Mahaffy, P. R.; Wong, A-S. “Methane and related trace species on Mars: Origin, loss, implications for life, and habitability.” Planetary and Space Science  hii  Methanogens Wiki


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