Use of natural products for the microorganisms removal from stone church cultural heritage

Biodeterioration of stone assets is a long term process produced by the microbial communities living and developing on the surface which release organic and inorganic acids, being involved in redox processes of the matrices constituents (bio-corrosion).The understanding of the complex interactions between colonizing organisms themselves, environmental pollutants and chemical degradation processes represent the necessary basis for the diagnostics of monuments degradation status and their specific maintenance. In recent years, the study of natural biocides able to selectively remove biological contamination from stone surfaces has intensified [1,2]. In particular, in this work, the biocidal activity of glycoalkaloids, inserted on proper gelling agents as supporters, was investigated.The use of a Polyvinyl alcohol hydrogel(PVA) based biocompatible gel, suitable to incorporate glycoalkaloids and which can be easily applied to the deteriorated stone artifacts, had been proposed for the bio-cleaning of cultural heritages. The study site was represented by the stone church of San Pietro Barisano (part of the UNESCO heritage) located in Matera (southern Italy) and specifically the hypogeum of the structure, where significant biodiversity was found. The first phase of the work was the investigation of biological communities present on the stone surface favoured by both the microclimate inside the church and the important infiltrations of water. The second phase of the work consisted in the sampling, isolation, identification and characterization of fungal species, present on the deteriorated surface. Preliminary identification, based on a single locus of the ribosomal RNA,(Internal Transcribed Spacer-ITS) reported the presence of few fungal genera such as Penicillum, Botryotrichum, Phialophora and Cladosporium. Further molecular identification and characterization at species level based on multilocus molecular analyses are in progress. Finally, the interesting part of the work concerned the optimization of the biogel composition to be used as a support for the glycoalkaloids extracted from the Solanum nigrum plant, in order to evaluate the biocidal activity on the identified microorganisms. The calcarenite samples characterization was performed by surface analysis using X-rays photoelectron spectroscopy (XPS), before and after the cleaning treatments to verify any alteration due to the gel application. Obtained results will be discussed according to close research literature findings.