Canvas paintings are among the most endangered works of cultural heritage, as they are traditionally made of natural materials that can be overgrown by fungi. The secretion of enzymes and acids can cause chemical and esthetic changes and thus reduce their value. In the restoration of paintings, supposedly less sensitive synthetic materials are often used, and their resistance to mold was investigated in this study. We found that the fungi causing visible changes to the paintings are xerotolerant/xerophilic molds, mainly from the genera Aspergillus and Penicillium, which grow in an environment with low relative humidity. Among the tested 55 fungal species isolated from canvas paintings, we found a diverse enzymatic activity of xerotolerant and a low specific enzymatic activity of obligate xerophilic fungi that can contribute to the degradation of most of the components of these artworks. Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) analysis of the infected synthetic materials revealed that strains Asp. puulaauensis (EXF-7678) and Asp. destruens (EXF-10360) are able to grow and/or degrade commonly used restorative materials, e.g. the adhesives Lascaux 498 HV and Lascaux 303 HV, the acrylic resin P550, the urea-aldehyde resin Laropal A81, the hydrocarbon resin Regalrez 1094 and BEVA 371. Analysis of the genome and transcriptome of selected species Aspergillus puulaauensis (EXF-7678), grown on the materials Lascaux 498 HV and Regalrez 1094, showed an increased expression of genes of some esterases and oxidases. The study represents the first fungal transcriptome analysis in the field of conservation-restoration, and the results provide a good basis for further research. At the same time, it is a proof of the harmfulness of xerophilic fungi for canvas paintings and a challenge to think about new measures in museums and painting depots, especially to reach the limit conditions for their growth.
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