Dominique Petrocchi

Weathering processes seriously affect the durability of outdoor marble monuments. In urban environments, a very common deterioration phenomenon is the dark discoloration or blackening of marble. This paper describes a multidisciplinary study on the state of conservation of white marbles of the Florence Cathedral and the microbial community involved in their deterioration. The study is focused on the widespread dark discoloration of marble analyzed in two differently exposed sites of the Cathedral. It aims to provide information useful for future interventions to control the microbial growth. By chemical and petrographic analysis, in situ and ex situ microscopy, and cultivation and identification of microorganisms, it was found that (i) the darkening is mainly due to the growth of black fungi and dark cyanobacteria and (ii) the state of conservation of marble and the growth pattern of microorganisms seems to be linked to the microclimatic conditions, in particular to solar radiation exposure. This is the first report on the lithobiontic community inhabiting the Florence Cathedral marbles, with a more detailed investigation of the culturable mycobiota.

Propolis is a resinous material produced by honeybees from different plant sources and used in the hive as a building material and to protect the colony from parasites and pathogens. Despite its antimicrobial properties, recent studies showed that propolis hosts diverse microbial strains, some with great antimicrobial potential. In this study, the first description of the bacterial community of propolis produced by the gentle Africanized honeybee was reported. Propolis was sampled from hives of two different geographic areas of Puerto Rico (PR, USA), and the associated microbiota investigated by both cultivation and metataxonomic approaches. Metabarcoding analysis showed appreciable bacterial diversity in both areas and statistically significant dissimilarity in the taxa composition of the two areas, probably due to the different climatic conditions. Both metabarcoding and cultivation data revealed the presence of taxa already detected in other hive components and compatible with the bee's foraging environment. Isolated bacteria and propolis extracts showed antimicrobial activity against Gram-positive and Gram-negative bacterial tester strains. These results support the hypothesis that the propolis microbiota could contribute to propolis' antimicrobial properties.

Pink discolorations are often observed on heritage buildings mainly in areas affected by salt weathering, where the development of halotolerant and halophilic microorganisms is favored. Part of these extremophilic microorganisms contains carotenoids, reason for which their colonization becomes visible by naked eye on large surfaces. This work investigates the pink alteration of the walls with drawings attributed to Michelangelo, located in the basement room of the Medici Chapel (Florence, Italy). The results of in-depth multidisciplinary investigations are discussed in the context of a thorough literature review on pink alterations of heritage buildings. For the first time, we combined culture-based approaches with metagenomic analyses that revealed the pink pigmented archaea Halalkalicoccus sp. as dominant, pointing their role in the pink discoloration present on the wall. Raman spectroscopy was exploited for the characterization of the biogenic pigments and Fourier Transform infrared spectroscopy and scanning electron microscopy to analyze the salt formations present on the walls.

Abstract This chapter illustrates the potential of using volatile binding media (VBM) in emergency contexts to secure works of art through a temporary consolidation that allows either a safe transport or an in-situ restoration. VBM are substances with adhesive and cohesive properties that at room temperature are solid, passing directly to the aeriform state by sublimation. They are requested to ensure adequate consolidation, to leave the composition, morphology, or structure of the object unaffected, and to be completely reversible. Cyclododecane (CDD) was extensively used in past decades, but, due to its recent limited availability, the identification of an alternative VBM is a challenging task. In this work, experimental activity focuses on characterizing the properties of either already known molecules (such as menthol) or less investigated materials (such as menthyl lactate). The application of VBM (melted or dissolved in solvents) on several substrates (wood, plaster, terracotta…) was explored to evaluate different parameters. These results will be useful to select the most adequate application protocol in different emergency contexts. Preliminary results of the use of the selected VBM on a wooden sculpture recovered after the 2016 earthquake are reported. Biocide activity of menthol, as a further property to secure artworks, was also studied.