Soil bacteria, coloured SEM. Bacillus cereus bacteria (blue) coating the surface of a stone monument (beige). Bacillus cereus is a common soil bacterium. It naturally secretes calcium carbonate to balance acidity. Scientists exploit this ability to aid the conservation of historic monuments. Bacillus cereus and other types of bacteria are applied to stone buildings and statues. The bacteria penetrate into the pores of the stone and secrete calcium carbonate, which helps to cement the stone together. Bacillus cereus has successfully been used to preserve monuments in France. Magnification unknown.