Calcium Carbonate Mineralization: Involvement of Extracellular Polymeric Materials Isolated from Calcifying Bacteria

Department of Basic and Applied Biology, University of L'Aquila, 67010 L'Aquila, Italy.
Microscopy and Microanalysis (Impact Factor: 1.88). 06/2012; 18(4):829-39. DOI: 10.1017/S1431927612000426
Source: PubMed


This study highlights the role of specific outer bacterial structures, such as the glycocalix, in calcium carbonate crystallization in vitro. We describe the formation of calcite crystals by extracellular polymeric materials, such as exopolysaccharides (EPS) and capsular polysaccharides (CPS) isolated from Bacillus firmus and Nocardia calcarea. Organic matrices were isolated from calcifying bacteria grown on synthetic medium--in the presence or absence of calcium ions--and their effect on calcite precipitation was assessed. Scanning electron microscopy observations and energy dispersive X-ray spectrometry analysis showed that CPS and EPS fractions were involved in calcium carbonate precipitation, not only serving as nucleation sites but also through a direct role in crystal formation. The utilization of different synthetic media, with and without addition of calcium ions, influenced the biofilm production and protein profile of extracellular polymeric materials. Proteins of CPS fractions with a molecular mass between 25 and 70 kDa were overexpressed when calcium ions were present in the medium. This higher level of protein synthesis could be related to the active process of bioprecipitation.

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Available from: Claudia Ercole, Jan 03, 2015
    • "Concerning CaCO 3 -precipitating bacteria and stone environments, to the authors' knowledge only one study has reported the effect of calcium on EPS production. In this study, the presence of 4 mM calcium ions in the culture medium increased biofilm formation by strains of Bacillus firmus and Nocardia calcarea isolated from an Italian karst cave (Ercole et al. 2012). The amounts of EPS and capsular polysaccharides (CPS) extracted from these strains were higher in the presence of calcium. "
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    • "Broadly speaking, differences in crystal morphology occur because of the presence and different concentrations of xanthan and amino acids. Experiments have also shown a direct relationship between cell growth and the presence of capsular polysaccharides (which compose a structural component of biofilms) [35] which may also help explain the structural network patterns found in our B. pasteurii sample. One of the reasons for this effect is likely to be that complex molecules found in the EPS bind to the surface of the crystal, either prompting or inhibiting crystal formation across specific faces of the crystal over specific times. "
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    • "The biofilm structure seems to be largely determined by the production of slime like matrix of EPS, which provides structural support for the biofilm. Ercole et al. 2012 also reported that deposition of carbonate crystals is promoted by EPS. "
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