Research on chromatic alterations of marbles from the fountain of Villa-Litta (Lainate, Italy)

The fountain of Galatea at Villa Litta (Lainate, Milan) showed abundant flowerings of black spots accompanied by little red spots on the marble surface. On these altered areas no chemolithotrophic bacteria were found, although many heterotrophic microorganisms were present. The high number of colonies of Alternaria alternata isolated by black spots may induce us to believe that this fungal strain is the cause of such alteration. From the red areas however, in spite of the high number of heterotrophic bacteria (10(6) CFU/g marble), only a few red pigmented microbial strains classified as Micrococcus roseus, Flavobacterium sp. and Rhodotorula minuta were isolated. The resonance Raman spectra carried out on the red spots showed the absence of carotenoids, whilst the normal Raman spectra showed the presence of minium (Pb3O4). The lead probably derives from the pipes of the fountain. Two biocides, Neo-Desogen and Cequartyl, were tested by minimum inhibitory concentration on the isolated microorganisms: R. minuta showed a higher sensitivity to both biocides compared with A. alternata, whilst M. roseus and Flavobacterium sp. showed more sensitivity towards Cequartyl. Three years after treatment with Neo-Desogen, small black and red spots were found. Microbiological analyses and ATP determination showed a new colonization of the heterotrophic bacteria (10(6) CFU/g) corresponding to the red spots, and of Mycetes (10(3) CFU/g) corresponding to the black ones