Natural Biocides to Prevent the Microbial Growth On Cultural Heritage

Many historic, cultural and artistic objects and buildings are made of stone. Like all materials, stone is subject to inexorable deterioration. Along with chemical and physical weathering factors, microbial growth plays an important role in this process. Stones type and local climatic differences have a great impact on the biodeterioration process and their outcomes. Microbial metabolism results in deteriorating agents such as organic and inorganic acid, chelating agents, enzymes and extracellular polymeric substances (EPS) causing e.g. biocorrosion and biomineralization; furthermore phototropic and heterotropic microorganism (ex. Firmicutes and fungi) are able to penetrate into stone mineral [1,2,3]. In addition to structural damage, rock biofilms cause aesthetic damage. In general the biocides used to prevent the growth of microbes are mostly based by using chemical methods, but they show a restricted efficiency and can cause discolorations and severe damages to the cultural heritage and ,also, they affect higher organisms including humans. Recently, the biotechnology and the applied microbiology (the use of antagonistic organisms or their metabolites products against the biodeteriorating agents) offers a wide range of new procedures for the cleaning and conservation of the artistic substrata [4-9]. The case of the study regards two historical bridges: the “San Vito Bridge” located in Potenza and “Della Vecchia Bridge” located in Campomaggiore, a little village near Potenza. The bacteria isolated belong to a wide variety of phylogenetic group being closely related to species of 10 genera within the Proteobacteria, the Firmicutes and the Actinobacteria; the number of fungi was slightly lower than those of bacteria. The fungi isolated on two bridges belong to Aspergillus, Penicillium and Stemphylium genera. In this work secondary metabolites of Burkholderia gladioli pv. agaricicola (Bga) ICMP 11096 strain and glycoalkaloids derived from Solanacee extracts, were used against bacteria and fungi isolated. Results show that all secondary metabolites inhibited in vitro and in vivo the growth of these colonising confirming that the application of biopesticides will be is a promising alternative to synthetic pesticides over traditional technologies. In fact, the use of these natural substances consents a more homogeneous removal of the surface deposits without compromising the substrata structure and the preservation of patina noble ; in addition, bio-cleaning has proven to be more selective than chemicals.