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, 73 (1), 271-7

Synthetic Consolidants Attacked by Melanin-Producing Fungi: Case Study of the Biodeterioration of Milan (Italy) Cathedral Marble Treated With Acrylics

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Synthetic Consolidants Attacked by Melanin-Producing Fungi: Case Study of the Biodeterioration of Milan (Italy) Cathedral Marble Treated With Acrylics

Francesca Cappitelli et al. Appl Environ Microbiol.

Abstract

Monuments and artistic stone surfaces are often consolidated and protected with synthetic polymers, in particular, acrylics. Although it is generally thought that acrylic polymers are resistant to biodeterioration, we report for the first time the systematic occurrence of dematiaceous meristematic fungi on many marble samples of the cathedral in Milan (Italy) previously treated with this material. Fourier transform infrared spectroscopy applied to the Milan cathedral stone samples revealed characteristic features of biodeteriorated synthetic resins that differentiated them from the aged but nonbiodeteriorated samples. Samples showing biological colonization were analyzed for the presence of fungi. Cultivation and morphological characterization and methods independent from cultivation, such as denaturing gradient gel electrophoresis coupled with partial 18S rRNA gene sequencing and immunofluorescence staining with melanin-binding antibodies, showed that melanin-producing species are heavily present on stone surfaces protected with acrylic resins. This observation raises the question of the effectiveness of acrylics in protecting stone artworks.

Figures

FIG. 1.
FIG. 1.
(a) Sample 14F033: FTIR spectrum image of a small quantity of orange film residue. (b) Sample 14F034: FTIR spectrum image of a pink-beige patina over calcite crystals. Scale bars, 500 μm.
FIG. 2.
FIG. 2.
FTIR spectrum of (a) a film of “Surface Clear Preserving Opaco” freshly cast on a sodium chloride window; (b) sample 14F033, representing marble microfragments with calcite crystals and residues of acrylic polymer seen as an orange thin film; and (c) sample 14F034, representing a biological patina on calcite crystals where the polymeric film is almost completely deteriorated.
FIG. 3.
FIG. 3.
(a) A chip of marble sample 19O029, with fungus coating part of the surface. The marble (arrowhead) did not fluoresce, whereas the fungal coat (arrow) fluoresced intensely. Scale bar, 20 μm. (b) A view (×20 magnification) of 13E036, with a magnified inset (×100). Scale bar, 10 μm.

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