The master's thesis describes microbiological analyses of wall paintings on the exteriors of churches in three different locations. The master's thesis is divided into a theoretical and practical part. The theoretical part consists of the presentation of locations and wall paintings from which we took samples from, that is, from visibly changed and with microbes covered parts of paintings. It also includes a review of the literature on microorganisms, which may damage wall paintings and other outdoor artworks, as well as an overview of the various methods by which microorganisms on wall paintings can be detected and identified.
The practical part presents the methods of taking samples from wall paintings and their further processing. When microbes were grown on the flat surface, samples were impressed on a transparent adhesive tape, and in cases of large volumetric growth, we scraped small pieces of paintings with scalpel. From the samples taken with adhesive tape and scalpel, the preparations were made and observed under the light microscope, and the scraps were observed under the stereo microscope. Microscopic preparations were observed in visible light, some also in fluorescent light. In the latter case, using fluorescent dyes we could separate living and dead cells. From the changed parts of the paintings, we used samples for cultivation, most often with non-invasive method by using swabs. We applied them to four different types of culture media: for the isolation of bacteria, archaea and fungi. From these media, pure cultures were isolated, DNA was extracted from selected cultures and DNA sequences important for identification were acquired. On the basis of these, microbes were identified by comparison of sequences with global DNA databases. Through experiments, we obtained an insight into the microbial communities on the surface and in depth of the paintings, and identified the organisms that can be cultivated in cultures. An easy method of microscopy with fluorescence dyes gave us an insight into the viability of the fungal community. Through the identification of microorganisms, we can get information about the impact they have on wall paintings. More data than we have about their identity and physiological properties, potentially help us to prevent their colonization by providing appropriate environmental factors. If the infection is already present, it is easier to identify the best methods and materials for conservation-restoration of the artwork after microorganisms' identification.