Induction of Calcium Carbonate by Bacillus cereus

Abstract

The purpose of this research was to study how the bacteria Bacillus cereus (DCB1) utilizes calcium ions in a culture medium with carbon dioxide (CO2) to yield calcium carbonate (CaCO3). The bacteria strain DCB1 was a dominant strain isolated from dolomitic surfaces in areas of Karst topographies. The experimental method was as follows: a modified beef extract-peptone medium (beef extract 3.0 g, peptone 10 g, NaCl 5.0 g, CaCl2 2.0 g, glass powder 2.0 g, distilled water 1 L, and a pH between 6.5 and 7.5) was inoculated with B. cereus to attempt to induce the synthesis of CaCO3. The sample was then processed by centrifugation every 24 h during the 7-day cultivation period. The pH, carbonic anhydrase (CA) activity, and the concentrations of both HCO- 3 and Ca2+ in the supernatant fluid were measured. Subsequently, precipitation in the culture medium was analyzed to confirm, or otherwise, the presence and if present, the formation, of CaCO3. Methods used included X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectroscopy (EDS). Meanwhile, the carbon source in the carbonate was classified by its isotope composition. Results showed that B. cereus can improve its pH value in this culture medium; concentrations of HCO- 3 and Ca2+ showed a significant decline over the duration of the cultivation period. CA activity reached its maximum during the second day; XRD, SEM, TEM, and isotope analysis all revealed the presence of CaCO3 as a precipitate. Additionally, these results did not occur in an aseptic control group: no detectable level of CaCO3 was produced therein. In conclusion: B. cereus can metabolize active materials, such as secretase, by its own growth and metabolism, and can either utilize atmospheric CO2, or respire, to induce CaCO3 production. Experimental evidence is offered for a concomitant CO2 reduction and CaCO3 induction by microorganisms.