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Microbial nucleation of Mg-rich dolomite in exopolymeric substances under anoxic modern seawater salinity; new insight into an old enigma

Stefan Krause, Volker Liebetrau, Stanislav Gorb, Monica Sanchez-Roman, Judith A. McKenzie and Tina Treude
Microbial nucleation of Mg-rich dolomite in exopolymeric substances under anoxic modern seawater salinity; new insight into an old enigma
Geology (Boulder) (May 2012) 40 (7): 587-590

Abstract

Sulfate-reducing bacteria are known to mediate dolomite formation under hypersaline conditions, but details of the crystal nucleation process are still poorly constrained. Our laboratory study demonstrates for the first time that Desulfobulbus mediterraneus, a marine sulfate-reducing bacterium, mediates primary precipitation of Mg-rich dolomite under anoxic conditions in media replicating modern seawater chemistry at low temperature (21 degrees C). Precipitation of crystals was associated with extracellular polymeric substances in a monospecific biofilm, providing templates for nucleation by altering the molar Mg/Ca ratio. After initial nucleation of single nanospherulites ( approximately 50 nm), growth was mediated by aggregation, resulting in spherulites of approximately 2-3 mu m in diameter. Nucleation led to differences in Mg/Ca ratios and delta (super 44/40) Ca values among the organic material (i.e., biofilm including cells and extracellular polymeric substances; 0.87+ or -0.01 [2 SD] and 0.48 per mil+ or -0.11 per mil [2 SE], respectively), the crystals (1.02+ or -0.11 [2 SD] and <-0.08 per mil+ or -0.24 per mil [2 SE], respectively), and the liquid bulk medium after mineral precipitation (4.53+ or -0.04 [2 SD] and 1.10 per mil+ or -0.24 per mil [2 SE], respectively). These data indicate a two-step fractionation process involved in the sequestration of Ca from the solution into the crystal lattice of the mineral precipitated. Our results demonstrate the capability of extracellular polymeric substances to overcome kinetic inhibition, fostering the formation of kinetically less favorable Mg-rich dolomite, and they also question the applicability of the Ca isotopic system as a proxy for paleogeochemistry of seawater.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 40
Serial Issue: 7
Title: Microbial nucleation of Mg-rich dolomite in exopolymeric substances under anoxic modern seawater salinity; new insight into an old enigma
Affiliation: Helmholtz Centre for Ocean Research Kiel (GEOMAR), Department of Marine Biogeochemistry, Kiel, Germany
Pages: 587-590
Published: 20120523
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 45
Accession Number: 2012-065474
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Depository Item 2012177; accessed on June 7, 2012
Illustration Description: illus. incl. 2 tables, 1 plate
Source Medium: WWW
Secondary Affiliation: Christian-Albrechts-University of Kiel, DEU, GermanyCSIC, Centro de Astrobiologia, ESP, SpainETH Zurich, CHE, Switzerland
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201234
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