Natural biocides and bio-calcite: innovative tools for cultural heritage

Abstract

Lithic artworks as churches, historical buildings and every usage object are our precious cultural heritage, memory of our past history step needed to build present and future. These artistic heritages with morphological, chemical and physical properties totally dissimilar make they a “unicum”, characterized by a specific vulnerability. Their decay is unavoidable, but it is a challenge for the humankind to protect and preserve them. Thus far, solutions for the safeguard of cultural heritage are usually based on chemical procedures to remove biodeteriogen agents, but these substances can be hazardous to the environment, to public health and to stone materials itself because it is not known about the consequences of repeated applications. Then the restoration methods require innovative approaches, eco-friendly and not harmful to human beings and the environment. Aiming at this objective a deeply study on two rupestrian churches located in Matera (Italy) was carried out in order to prevent and/or control microbial and biological evolution, and to exploit the potential of some bacterial species in the interventions of stone consolidation. Surface analyses of detached rocks to evaluate the (i) stone composition, (ii) isolation and characterization of biological and (iii) microbial colonizers present on the stone surfaces were formerly performed. In vitro bioactivity test against autotrophic/heterotrophic species isolated was carried out using secondary metabolites extracted from cultivated crops and spontaneous herbs with a strong biocidal activity (extracts from Solanum nigrum, Volutaria lippii, Moricandia arvensis, Pulicaria inuloides). Finally, calcinogenic activity tests employing native bacteria (Bacillus strains) isolated on stone surfaces of the two churches constitute the conclusive research step. Glycoalkaloids inhibited all bacterial strains tested. Some strains of Bacillus to produce the greatest amount of crystals, coherent with the stone substrate, was evidenced. This research highlights the opportunity to change the way of thinking and performing recovery actions for cultural heritage. Not last-minute remediation but continuous monitoring and time by time actions to avoid the formation of aggressive colonisations.