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Transcript of Motivation
Dr. Werner Eckert
Prof. Ariel Kushmaro
Dr. Orit Sivan
Itay Bar Or
The Ph.D work of
Anaerobic methane oxidation via iron reduction is not a myth, but what is it?
Increase of methane gas
Microbial methane production (methanogenesis) occurs in anaerobic environments by Archaea.
Methanogenesis presumably starts when sulfate concentration is low.
Fractionation in methanogenesis
Fractionation of methanotrophy
Two archaeal lipids (archaeol and hydroxyarchaeol) gathered from marine sediment were found with very depleted isotopic values (~ -100‰). (Hinrichs et al.,1999)
Three groups of archaea (named ANME-1, ANME-2, and ANME-3) have been found to perform AOM. (Orphan et al.,2001)
For microbiologists geochemical evidences weren't enough. In order to find the microorganisms involve in AOM 3 methods mainly were used:
1) Lipids (Organic Geochemistry)
2) Microbial molecular methods (Nano SIMS-FISH,16S rRNA genes, etc.)
3) Functional genes (MCR, pMMO DSR)
DSR: Dissimilatory (bi)Sulfite Reductase is the last step of sulfate reduction. This gene encode the α and β subunits of the dsrAB
2)Identify the electron acceptor (in situ profiles, core and slurry experiments).
Using geochemical approach. (slurry experiments)
3)What is the mechanism?
1)To confirm the suggested deep AOM (in situ profiles, core and slurry experiments).
Using organic geochemistry approach (lipid analysis)
Using molecular microbial approach. (16S rRNA gene sequencing , qPCR)
Study site:Lake Kinneret
21 km long, 13 km wide, and a maximum depth of approximately 40 m.
A warm monomictic subtropical lake that is stratified during April-November.
Presence of methane, sulfate and iron.
Profiles indicating AOM
Methane concentration decreases below 20cm.
δ¹³C of methane increases due to biological consumption of depleted methane below 20 cm.
δ¹³C of TLE decreases below 20 cm due to production of light biomass
Suspected electron acceptors
Oxygen and Nitrate is absent in the sediment.
Sulfate concentration is depleted in the upper 10cm (the main AOM electron acceptor).
Ferrous concentration increases below 20cm.
Manganese oxide concentrations are very low, however it may be also a potential electron acceptor in AOM.
Amorphous Fe(III) enrichment incubation
Lipids extraction was divided to 5 fractions:
1)Asphaltene (not analyzed yet)
Fatty acids profile lipids
Bacterial lipids showed the most depletion in values.
Archeaol (ANME lipid) was detected in low concentration but with -21%
Rapid sedimentation rate together with insufficient decrease in isotopic values gives inconclusive results but no ANME involvement in LK.
Various iron minerals slurry experiments
Molecular microbial analysis
Sampling for microbial ecology
pmoA is present in the deep section of the sediment
Classification of archaeal sequences using SILVA ngs pipeline. Phyla and order distributions of sequences of the 454 sequencing above 1% at the different depths in the communities
is increasing with depth
Classification of bacterial sequences using SILVA ngs pipeline. Phyla and class distributions of sequences of the 454 sequencing above 1% at the different depths in the communities.
when amorphous iron is added methane concentration decreases
Ferrous iron (II) concentration increase after the addition of amorphous iron(III)
Hematite and magnetite show increase in methanotrophy.
BES inhibits methanogens activity
AOM did not stop it was increased.
Molybdate is inhibitor of sulfate reduction however its increases methanotrophy
Molybdate inhibits the sulfur cycle which is coupled to iron reduction. This leaves the iron oxides available to AOM.
dsrA is the highest in the middle section but still have high numbers in the bottom even though no sulfate is detected.
mcrA is in high numbers in the middle and bottom sections
MBG-D (Thermoplasmatales)could be a unique iron reducer methanotrophy
Some sequences of the Deltaproteobacteria class could be involved in indirect mechanisms of disproportionation of sulfur.
Nitrospira are increasing with depth and could oxidize ammonium/methane, some can reduce iron.
Thank you for listening
Thanks to my sponsors
Thanks to my supervisors
Thanks to all my lab friends
Thanks to my parents
Thanks to my family
Wuebbles and Hayhoe, 2002
Wuebbles and Hayhoe, 2002
To investigate the AOM process in fresh water sediment where sulfate concentrations are very low
iron mineral additions
BES= methanogenesis inhibitor
Molybdate= sulfate reduction inhibitor
Anaerobic oxidation of methane (AOM)
Mehane emissions from the various environments
2/3 of the total methane emission
1/3 of the total methane emission
Recent study shows that up to 90% of the methane produced in marine environment is oxidized before its emission to the atmosphere.
1) AOM is conclusivly shown.
2) AOM is a microbial process.
3) AOM is
preformed by sulfate reduction.
4) Methanogens/bacterial consortia are involved in AOM.
5) Competitive faster iron reduction pathway is utilizing the more available iron oxides.
6) AOM via iron reduction is a slow process which utilizes the less reactive iron oxides.
7) Iron and sulfur cycles are connected (not related to methane) even though sulfate concentration is below detection limit.
AOM via iron reduction was evident in Lake Kinneret by insitu profiles, top core experiments and slurry experiments.
In natural conditions less reactive iron oxides are used for AOM.
A cryptic sulfur - iron coupling competes with this process.
Lipid analysis did not detect any ANME
Functional genes showed that SRB and aerobic methanotrophs are present in the deep sediment
Methanogens are the main suspects for been methanotrophs.
Possible direct process could be through new, currently unknown bacteria/archaea that reduce iron and utilize methane.
Indirect processes could include (1) reduction fo Fe(III) by utilizing hydrogen which could consume most of the produced hydrogen and create an effect of "reverse methanogenesis" by methanogens.
(2) an oxygenic methane oxidation pathway in an anaerobic environment, when methane is oxidized by oxygen that is released from iron oxides or other intermediates.
oxidizes up to 90% of the methane
Recent study (Segarra et al 2015) showed that AOM is a critical process also in fresh water sediments, and oxidizes over 50% of the produced methane.
The most probable electron acceptor is iron!
This iron driven AOM is not through sulfate.
Metanogens are involved