An interdisciplinary study of biodeterioration of the external marbles of Santa Maria del Fiore Cathedral, Florence (IT)

Stone-built cultural heritage exposed to urban environment represents a habitat where heterogeneous microbial communities can grow causing structural and aesthetical modifications and significant biodeterioration phenomena, the most common being colored patinas and crusts. An in-depth investigation of microbial community composition and its metabolic potential is essential to take the appropriate measures to control its growth. Conventional biocides remain the most used practical solution to control microbial growth, nevertheless, they may be dangerous for human health and the environment. The Cathedral of Santa Maria del Fiore (SMFC) is a major architectural masterpiece in Florence (IT), and its conservation is a main issue of worldwide concern. The whole edifice is externally covered with polychrome stone panels consisting of white marbles, serpentinites and red limestones. Here we report a multidisciplinary investigation on the state of conservation of SMFC white marbles which show, in some extended areas, patinas and discoloration due to microbiological growth. This work provides new details on the deterioration of SMFC marble and, for the first time, on the microbial community involved. This preliminary knowledge will be used for planning field tests with innovative low environmental impact biocides, such as essential oils, to contrast biodeterioration.