Calcium carbonate crystal deposition is a very diffuse phenomenon that has been described for many microorganisms living in different environments. Nevertheless, the actual molecular mechanisms by which bacteria foster calcium carbonate precipitation are not known. A better understanding at the molecular and genetic levels could improve our knowledge of the process and be useful for biomineralization applications such as conservation of calcareous monumental stones. In this work we report preliminary data obtained with two experimental approaches. The genetic approach, based on the analysis of Bacillus subtilis mutants impaired in calcium carbonate crystal production, suggested a link between calcium precipitation and intermediate(s) of fatty acids metabolism. To investigate the role of cell structures we developed an in-vitro test. In this test dead bacterial cells induce calcium carbonate precipitation; moreover, cells from active calcinogenic strains showed a much higher and/or faster production of CaCO3 crystals than did less active strains.