STONE AUTOCHTHONOUS MICROORGANIMS: AN EFFICIENT HELP ON HISTORICAL STONE-BUILDINGS BIO-RESTORATION

Different microorganisms in addition to lichens and algae, can cause problems to the conservation of cultural heritage because of their bio-deteriorative potential. This holds true for all types of historic artifacts, and even for art made of modern materials in public buildings, museums etc. The variety of bio-deterioration phenomena observed on materials of cultural heritage is determined, also, by several factors, such as the chemical composition and nature of the material itself, climate and exposure of the object, biological colonizers. The synergistic actions of all these factors can cause not only aesthetic deterioration of the cultural heritage but also structural damages. Currently, studies are focused towards the use of living organisms as antagonist of destructive colonizers (algae or fungal colonies) or as producers of biocalcite to restore the surface of stones. In previously published works we showed the cleaning bioactivity of secondary metabolites produced by bacteria and vegetables (Caligine et al., 2013; Sasso et al., 2013) on two bridges located in two different places close to Potenza (South Italy). Successively, we identified and cultured several bacterial colonies, collected from the same bridges, belonging mostly to the genus Bacillus, which is known as an organism having 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 of destructive organisms, we decided to test the effectiveness of some 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. Among all autoctonous bacteria tested, Bacillus thuringiensis worked as the best producer of biocalcite. These results encouraged strongly our research: our aim is actually the implementation of new bio-restoration methods of cultural heritage reducing maintenance intervals and costs: "adopt a monument and take care of it with love"