Xerophilic fungi contaminating historically valuable easel paintings from Slovenia

A novel contaminant in museums? A cross-sectional study on xerophilic Aspergillus growth in climate-controlled repositories

In the last decade, extensive fungal growth has developed in Danish museums parallel to climate change, challenging occupational health and heritage preservation. The growth was unexpected as the museums strived to control relative humidity below 60 %, and it should exceed 75 % to risk growth. A Danish case study found xerophilic Aspergillus species able to grow at low relative humidity in a museum repository. This cross-sectional study aimed to examine whether xerophilic growth from Aspergillus section Restricti has become a novel contaminant nationally distributed in Danish museum repositories striving to control relative humidity according to international environmental recommendations for heritage collections. The study examined The National Museum of Denmark and eight large State Recognized museums distributed throughout Denmark. It was based on 600 swab and tape-lift samples and 60 MAS100-Eco and filter air samples analyzed for fungi with cultivation and morphological identification, Big-Dye-Sanger sequencing, CaM-Nanopore and ITS-Illumina amplicon sequencing. The study showed growth from seven xerophilic Aspergillus species: A. conicus, A. domesticus, A. glabripes, A. halophilicus, A. magnivesiculatus, A. penicilloides, A. vitricola, of which three are new to Denmark, and 13 xerotolerant Aspergillus species. There was no growth from other fungal species. The multiple detection approach provided a broad characterization; however, there was variance in the detected species depending on the analysis approach. Cultivation and Big-Dye Sanger sequencing showed the highest Aspergillus diversity, detecting 17 species; CaM-Nanopore amplicon sequencing detected 12 species; and ITS-illumina amplicon sequencing detected two species but the highest overall diversity. Cultivation, followed by Big-Dye Sanger and CaM-amplicon sequencing, proved the highest compliance. The study concluded that xerophilic Aspergillus growth is nationally distributed and suggests species from Aspergillus section Restricti as a novel contaminant in climate-controlled museum repositories. To safeguard occupational health and heritage preservation research in sustainable solutions, avoiding xerophilic growth in museum collections is most important.

Fungal Biodeterioration Risk in Monastic Libraries without Climate Control

Fungi have always posed an unquestionable threat to heritage collections worldwide. Now, in a future of climate change, biological risk factors may have to be considered even more than before. Models and simulations to assess possible impacts a changing outdoor climate will have on indoor environments and, in turn, on biodeterioration are still underdeveloped and require a more substantial data basis. This study aimed at filling some of these knowledge gaps through a broad-based approach combining microclimatic and microbiological monitoring in four historic libraries in Austria with an uncontrolled indoor climate: Altenburg Abbey, Melk Abbey, Klosterneuburg Monastery and the Capuchin Monastery in Vienna. Data were generated from thermohygrometric sensors, cultivation-dependent air- and surface sampling and further surface dust sampling for cultivation-independent analyses. Results gave insights on the status quo of microbiological loads in the libraries and outdoor-indoor relationships. Influences of the geographic location and room-use on corresponding indoor fungal profiles were identified. Lower fungal diversities were found at the most rural site with the strongest climatic fluctuations and extreme values than in the most urban, sheltered library with a very stable climate. Further, the humidity-stabilizing potential of large collections of hygroscopic materials, such as books, was also examined. Implications for a sustainable approach to prevent future biodeterioration are discussed, supporting the long-term preservation of these valuable historic collections.

Degradation Potential of Xerophilic and Xerotolerant Fungi Contaminating Historic Canvas Paintings

Fungi are important contaminants of historic canvas paintings worldwide. They can grow on both sides of the canvas and decompose various components of the paintings. They excrete pigments and acids that change the visual appearance of the paintings and weaken their structure, leading to flaking and cracking. With the aim of recognizing the most dangerous fungal species to the integrity and stability of paintings, we studied 55 recently isolated and identified strains from historic paintings or depositories, including 46 species from 16 genera. The fungi were categorized as xero/halotolerant or xero/halophilic based on their preference for solutes (glycerol or NaCl) that lower the water activity (aw) of the medium. Accordingly, the aw value of all further test media had to be adjusted to allow the growth of xero/halophilic species. The isolates were tested for growth at 15, 24 °C and 37 °C. The biodeterioration potential of the fungi was evaluated by screening their acidification properties, their ability to excrete pigments and their enzymatic activities, which were selected based on the available nutrients in paintings on canvas. A DNase test was performed to determine whether the selected fungi could utilize DNA of dead microbial cells that may be covering surfaces of the painting. The sequestration of Fe, which is made available through the production of siderophores, was also tested. The ability to degrade aromatic and aliphatic substrates was investigated to consider the potential degradation of synthetic restoration materials. Xerotolerant and moderately xerophilic species showed a broader spectrum of enzymatic activities than obligate xerophilic species: urease, β-glucosidase, and esterase predominated, while obligate xerophiles mostly exhibited β-glucosidase, DNase, and urease activity. Xerotolerant and moderately xerophilic species with the highest degradation potential belong to the genus Penicillium, while Aspergillus penicillioides and A. salinicola represent obligately xerophilic species with the most diverse degradation potential in low aw environments.