Implementation of new bio-restoration methods of historical stone-buildings based on autochthonous microorganims

The biological colonization of stone buildings and artefacts is responsible of aesthetic deterioration and can cause structural damages. Many organisms, such as phototropic ones, may use the stone as a support and successively they can favour more complex colonization with possible biodeterioration effects. The colonization it is always related to the type of rocks and the localisation area, and is influenced by the microclimate and the biodiversity of the airflora/airfauna. These organisms are able to use the stone mineral components and the surface deposits, exerting a detrimental effect on stone material by their metabolic activity. Currently, studies are directed towards the use of living organisms as antagonist of destructive colonizers (algae or fungal colonies) or as producers of biocalcite to re-construct the surface of stones. In a previous work we showed the cleaning bioactivity of secondary metabolites produced by Burkholderia gladioli pv agaricicola (Bga) ICMP 11096 strain, glycoalkaloids extracted from Solanacee and peptaibols produced by Trichoderma sp. against some native bacterial and fungal colonies found on the stones of two bridges located near Potenza (Suth Italy). Successively, we identified and cultured several bacterial colonies, collected from the stones of the same bridges, and belonging mostly to the genus Bacillus, which is known as an organism showing a specific ability to induce the precipitation of minerals, especially calcite. Having in mind that the natural formation of biocalcite can reduce, and successively limit the bio-contamination and infestation by destructive organisms, we decided to test some of the identified bacterial species . The experiments, carried out in vitro by using calcium acetate as source of Ca showed the formation of well-defined biocalcite crystals resulting by FT-IR spectrophotometry, Xray diffraction analysis, and SEM coupled with EDS analysis. Bacillus thuringiensis looked as the best producer of biocalcite. These results are very encouraging for our research aiming at the implementation of new bio-restoration methods of historical stone-buildings based on autochthonous microorganism reducing maintenance intervals and costs.