ABSTRACT
Conservative treatment of calcareous stone can be obtained by exploiting calcium carbonate crystal precipitation by bacteria. The development of a biomineralization stone treatment in absence of living cells could be a more suitable biotechnological tool than the application of living cultures of calcinogenic bacteria. The isolation of mutant strains of Bacillus subtilis unable to induce crystal formation suggests that bacterial cells play an active role in this process and that mineral formation is not only an indirect consequence of environmental changes produced by the metabolic activity of bacteria. Stone samples treated with B. subtilis cells show a reduction in stone porosity, as verified with capillary water absorption tests. In fact, chemical reactions with stone minerals due to metabolic by-products and the growth of fungi, because of the application of organic nutrients for bacterial development, can have negative effects on the stone itself.
