4.7 Article

Bacterial extracellular polymeric substances (EPS) mediate CaCO3 morphology and polymorphism

Journal

CHEMICAL GEOLOGY
Volume 262, Issue 3-4, Pages 138-146

Publisher

ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemgeo.2009.01.006

Keywords

Bacteria; EPS; Biomineralisation; Calcium carbonate

Funding

  1. School of GeoSciences Teaching Studentship

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The effect of bacterial extracellular polymers (EPS) on calcium carbonate morphology and polymorphism was investigated by means of free-drift mineralisation experiments, conducted using cells of the EPS-producing thermotolerant Bacillus licheniformis S-86. The cells either had the EPS layer intact (native cells) or had the EPS layer removed (EPS-free cells). Experiments were also undertaken in the absence of cells, but with the addition of the extracted EPS solution. It was found that the abiotic control and EPS-free cell experiments contained vaterite and calcite when sampled after 12 h and 48 h, whereas the native cell and EPS-solution experiments contained only calcite. These results suggest that the presence of EPS inhibits vaterite precipitation. It is proposed that dissolved organic carbon (DOC) released from the EPS complexes Ca2+ ions in solution, reducing the calcium carbonate saturation and favouring calcite precipitation over vaterite. After 7 days, all experiments contained only calcite. However, distinct morphological differences between the calcite crystals precipitated in the four experiments were preserved after a period of 7 days, suggesting that crystal morphology may indicate the biological conditions under which calcite precipitated. (C) 2009 Elsevier B.V. All rights reserved.

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