Diversity and metabolic profile of the microbial communities inhabiting the darkened white marble of Florence Cathedral

Stone-built cultural heritage exposed to urban environment is a habitat where heterogeneous microbial communities grow, inducing significant biodeterioration. The conservation of the Cathedral of Santa Maria del Fiore in Florence is a main issue of worldwide concern. We previously investigated the dark discoloration of the external white marble and the associated microbiota in two study sites of Florence Cathedral, one northwest and the other southeast exposed, through microscopy and cultivation-dependent methods. The aim of this study was to obtain a more in-depth characterization of the microbial communities inhabiting marble in these two areas. Bacterial and fungal diversity was investigated through DNA metabarcoding of the 16S rRNA gene and ITS region, respectively. Furthermore, the metabolic activity of the entire microbial community was analyzed through Biolog™ Ecoplate technology, a tool rarely used in the investigation of biodeterioration. The taxonomic analysis evidenced a different structure of the communities in the two study sites. The Phenotype Microarray assay showed different metabolic profiles, with a higher metabolic potential of the southeast community. Cultivated bacteria showed the capacity for carbonate dissolution and precipitation.