Document Detail

Microorganisms metabolizing on clay grains in 3-km-deep Greenland basal ice.
MedLine Citation:
PMID:  16551227     Owner:  NLM     Status:  MEDLINE    
We have discovered > 10(8) microbial cells/cm3 attached to clay grains in the bottom 13 m of the GISP2 (Greenland Ice Sheet Project) ice core. Their concentration correlates with huge excesses of CO2 and CH4. We show that Fe-reducing bacteria produce most of the excess CO2 and methanogenic archaea produce the excess CH4. The number of attached cells per clay grain is proportional to grain perimeter rather than to area, which implies that nutrients are accessed at grain edges. We conclude that Fe-reducing microbes immobilized on clay surfaces metabolize via "shuttle" molecules that transport electrons to grain edges, where they reduce Fe(III) ions at edges to Fe(II) while organic acid ions are oxidized to CO2. Driven by the concentration gradient, electrons on Fe(II) ions at grain edges "hop" to Fe(III) ions inward in the same edges and oxidize them. The original Fe(III) ions can then attach new electrons from shuttle molecules at the edges. Our mechanism explains how Fe-reducers can reduce essentially all Fe(III) in clay minerals. We estimate that the Fe(III) in clay grains in the GISP2 silty ice can sustain Fe-reducing bacteria at the ambient temperature of -9 degrees C for approximately 10(6) years. F420 autofluorescence imaging shows that > 2.4% of the cells are methanogens, which account for the excess methane.
H C Tung; P B Price; N E Bramall; G Vrdoljak
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  Astrobiology     Volume:  6     ISSN:  1531-1074     ISO Abbreviation:  Astrobiology     Publication Date:  2006 Feb 
Date Detail:
Created Date:  2006-03-22     Completed Date:  2006-05-25     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  101088083     Medline TA:  Astrobiology     Country:  United States    
Other Details:
Languages:  eng     Pagination:  69-86     Citation Subset:  IM    
Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720, USA.
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MeSH Terms
Aluminum Silicates
Archaea / isolation & purification,  metabolism
Bacteria / isolation & purification,  metabolism
Electron Transport
Iron / metabolism
Methane / metabolism
Microscopy, Electron, Scanning
Microscopy, Fluorescence
Solar System
Water Microbiology*
Reg. No./Substance:
0/Aluminum Silicates; 0/Ice; 1302-87-0/clay; 74-82-8/Methane; 7439-89-6/Iron

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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