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| Titel |
Quantification of microbial activity in subsurface environments using a hydrogenase enzyme assay |
| VerfasserIn |
R. R. Adhikari, J. Nickel, J. Kallmeyer |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065745
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| Zusammenfassung |
| The subsurface biosphere is the largest microbial ecosystem on Earth. Despite its large
size and extensive industrial exploitation, very little is known about the role of
microbial activity in the subsurface. Subsurface microbial activity plays a fundamental
role in geochemical cycles of carbon and other biologically important elements.
How the indigenous microbial communities are supplied with energy is one of
the most fundamental questions in subsurface research. It is still an enigma how
these communities can survive with such recalcitrant carbon over geological time
scales.
Despite its usually very low concentration, hydrogen is an important element in
subsurface environments. Heterotrophic and chemoautotrophic microorganisms use hydrogen
in their metabolic pathways; they either obtain protons from the radiolysis of water and/or
cleavage of hydrogen generated by the alteration of basaltic crust, or they dispose of protons
by formation of water.
Hydrogenase (H2ase) is a ubiquitous intracellular enzyme that catalyzes the
interconversion of molecular hydrogen and/or water into protons and electrons. The protons
are used for the synthesis of ATP, thereby coupling energy-generating metabolic processes to
electron acceptors such as carbon dioxide or sulfate. H2ase activity can therefore be used
as a measure for total microbial activity as it targets a key metabolic compound
rather than a specific turnover process. Using a highly sensitive tritium assay we
measured H2ase enzyme activity in the organic-rich sediments of Lake Van, a saline,
alkaline lake in eastern Turkey and in marine subsurface sediments of the Barents Sea.
Additionally, sulfate reduction rates (SRRs) were measured to compare the results of
the H2ase enzyme assay with the quantitatively most important electron acceptor
process.
H2ase activity was found at all sites, measured values and distribution of activity varied
widely with depth and between sites. At the Lake Van sites H2ase activity ranged from ca. 20
mmol H2 cm-3 d-1 close to the sediment-water interface to 0.5 mmol H2 cm-3
d-1 at a depth of 0.8 m. In samples from the Barents Sea H2ase activity ranged
between 0.1 to 2.5 mmol H2 cm-3 d-1 down to a depth of 1.60 m. At all sites the
SRR profile followed the H2ase activity profile until SRR declined to values close
to the minimum detection limit (~10 pmol cm-3 d-1). H2ase activity increased
again after SRR declined, indicating that other microbial processes are becoming
quantitatively more important. The H2ase and SRR data show that our assay has a
potential to become a valuable tool to measure total subsurface microbial activity. |
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