Nanoscale Detection of Organic Signatures in Carbonate Microbialites

Microbialites are sedimentary deposits associated with microbial mat communities and are thought to be evidence of some of the oldest life on Earth. Despite extensive studies of such deposits, little is known about the role of microorganisms in their formation. In addition, unambiguous criteria prov...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2006-06, Vol.103 (25), p.9440-9445
Main Authors: Benzerara, Karim, Menguy, Nicolas, López-García, Purificación, Yoon, Tae-Hyun, Kazmierczak, Józef, Tyliszczak, Tolek, Guyot, François, Brown, Gordon E.
Format: Article
Language:English
Subjects:
Aragonite
Calcium carbonates
CARBONATES
Condensed Matter
Crystals
DETECTION
GEOSCIENCES
Materials Science
MICROORGANISMS
Mineral precipitation
Mineralogy
Minerals
Molecules
NANOSTRUCTURES
Nanotechnology
ORGANIC MATTER
Other,OTHER
Physical Sciences
Physics
Polysaccharides
Sediments
Spectroscopy
Studies
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Summary:Microbialites are sedimentary deposits associated with microbial mat communities and are thought to be evidence of some of the oldest life on Earth. Despite extensive studies of such deposits, little is known about the role of microorganisms in their formation. In addition, unambiguous criteria proving their biogenicity have yet to be established. In this study, we characterize modern calcareous microbialites from the alkaline Lake Van, Turkey, at the nanometer scale by combining x-ray and electron microscopies. We describe a simple way to locate microorganisms entombed in calcium carbonate precipitates by probing aromatic carbon functional groups and peptide bonds. Near-edge x-ray absorption fine structure spectra at the C and N K-edges provide unique signatures for microbes. Aragonite crystals, which range in size from 30 to 100 nm, comprise the largest part of the microbialites. These crystals are surrounded by a 10-nm-thick amorphous calcium carbonate layer containing organic molecules and are embedded in an organic matrix, likely consisting of polysaccharides, which helps explain the unusual sizes and shapes of these crystals. These results provide biosignatures for these deposits and suggest that microbial organisms significantly impacted the mineralogy of Lake Van carbonates.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0603255103