Bacterially induced mineralization of calcium carbonate: the roleof exopolysaccharides and capsular polysaccharides.

Abstract: Bacterially induced carbonate mineralization has been proposed as a new method for the restoration of limestones in historic buildings and monuments. We describe here the formation of calcite crystals by extracellular polymeric substances isolated from Bacjllus firmus and Bacjllus sphaerjcus. We isolated bacterial outer structures (glycocalix and parietal polymers), such as exopolysaccharides (EPS) and capsular polysaccharides ( CPS) and checked for their intluence on calcite precipitation. CPS and EPS extracted from both B. firmus and B. sphaerjcus were able to mediate CaCO3 precipitation jn vjtro. X-ray microanalysis showed that in all cases the formed crystals were calcite. Scanning electron microscopy showed that the shape of the crystals depended on the fractions utilized. These results suggest the possibility that biochemical composition of CPS or EPS intluences the resulting morphology of CaCO3. There were no precipitates in the blank samples. CPS and EPS comprised of proteins and glycoproteins. Positive alcian blue staining also reveals acidic polysaccharides in CPS and EPS fractions. Proteins with molecular masses of 25-40 kDa and 70 kDa in the CPS fraction were higWy expressed in the presence of calcium oxalate. This high level of synthesis could be related to the binding of calcium ions and carbonate deposition. Key words: bacteria glycocalyx, calcite precipitation, historic monument protection, calcifying bacteria, SEM