Xerophilic fungi have a taste for Danish art and cultural heritage

This pilot study examines the fungal colonisation of Anchers House, the Art Museums of Skagen, the former home of one of the most recognised couples in Scandinavian art history, Anna and Michael Ancher. The examination showed hyaline and white fungal colonies on museum artefacts but not on building structures and interiors. Analyses of air and surface samples showed growth of the xerophilic Aspergillus halophilicus, A. penicilloides, and A. magnivesiculatus able to grow at low water activity corresponding to low relative humidity (RH). Fungal colonisation adversely affects heritage preservation, occupational health, and audience access. Colonisation is hard to prevent because the xerophilic fungi can grow at RH as low as 58%, and the building is listed with heritage restrictions obstructing climate control. Peer-review under the responsibility of the organizing committee of the ICMB23.


Introduction
Museums are committed to preserving cultural heritage for posterity and communicating it to the public.Heritage preservation may be supported by controlling the indoor environment according to the acknowledged guidelines for museums advising stable climate within variations of the interval RH 35-65% and T 15-25 o C [1][2].Worldwide, museums attempt to meet these guidelines; however, variations in national location, building stock and climate control systems may lead to different levels of control.Some museums are obliged by legislation making it difficult to comply with the guidelines, which is the case of Anchers House, the main character of this study.In Anchers House, the artefacts and the building authenticity are to be preserved, obstructing mechanical climate control, an inbuilt problem in a draughty building where infiltration may cause elevated RH and fungal growth.
Recognised preventive conservation literature agrees that RH must exceed 70-75% if fungal growth is to occur [3][4].However, in the last decade, the growth of xerophilic fungi from Aspergillus section Restricti has occurred in Danish museum repositories with RH below 60% [5][6].These fungi are characterised by the ability to grow at a low water activity (aw), corresponding to low RH [7].It is not known if xerophilic fungi are also causing growth in the exhibitions of Historic House Museums.
This pilot study examines the fungal colonisation of Anchers House, the Art Museums of Skagen, the home of one of the most recognised couples in Scandinavian art history, Anna and Michael Ancher (Figure 1).The pilot study examined if the colonisation was due to xerophilic or other indoor fungi and discussed fungal detection, growth conditions, hazards, and prevention.

Materials and methods
The study included 1) building inspection and 2) fungal surface and air sampling and laboratory analysis.The building envelope was inspected, and data logging of RH and T in 2021-2022 was acquired.Air and surface temperature were measured, as well as moisture content (MC) in building structures.Fungal colonies on three artefacts were sampled with a) tape-lift transferred to slides for microscopy and b) sterile rayon swabs inoculated on two agar media (DG18 and the low aw agar MY50G).After incubation, the cultures were isolated, and species identification was determined by comparing morphology with reference fungi [7][8].Air sampling was conducted with MAS-100-ECO on DG18-agar and MY50G-agar.The air samples were processed as the surface samples, and the fungal concentration was presented as CFU/m 3 .

Results
The building envelope inspection showed degraded sills, brickwork joints, and leaking drainpipes.However, there was no discolouration from moisture on building structures (Figure 1), and MC at the leaks was only slightly elevated.Data logging showed annual variations of RH 35-65% and T 18-22 o C, supported by the point measurements, with short periods of RH 76%.No fungal growth was observed on the building structures, nor by the leaks in the building envelope.The growth was only on the museum artefacts, appearing as white and hyaline colonies (Figure 1).Tape-lift samples showed Aspergillus spp.producing conidiophores and ascomata (Figure 1).Artefact samples showed no Aspergillus cultures on DG18; in contrast, Aspergillus cultures developed on MY50G identified to A. halophilicus, A. penicilloides, A. magnivesiculatus, and Aspergillus spp.Cultivation and isolation of the MAS-100-ECO air samples on DG18 and MY50G showed 16 fungal species (Figure 2).The xerophilic species A. halophilicus, A. penicilloides, and A. magnivesiculatus primarily grew on MY50G with low aw.The highest species richness was on DG18 (p=0.0078),dominated by the growth of common indoor fungal species.However, the total concentration of fungi (CFU/m 3 ) was significantly higher on the low aw agar MY50G than on DG18 (ps<0.05).

Discussion
This pilot study showed xerophilic fungal growth on museum artefacts from Anchers House.The fungal species belong to the Aspergillus section Restricti characterised by the ability to grow at low aw corresponding to low RH.
It is unclear when the fungal colonisation developed, which is not remarkable, as a characteristic of the xerophilic fungi is slow growth of white and hyaline colonies [7], making the colonies less noticeable.The study did not determine what specifically initiated the growth; however, Anchers House is considered a draughty building, and the RH data loggings documented infiltration causing periodically elevated RH.It is well known that elevated RH may cause fungal germination and growth.
The fungal growth in Anchers House behaved similarly to studies in museum repositories (Bastholm et al. 2022 and2021), where only the museum artefacts were colonised, not the building structures.However, in Anchers House, the growth was isolated to museum artefacts made of paper and leather, unlike Bastholm et al., where artefacts in inorganic materials were also affected.It is considered that other heritage materials in Anchers House could also have been colonised under the right conditions.
Cultivation of the artefact samples showed mainly growth on MY50G.The significantly higher concentration on MY50G than on DG18 reflected that the fungi on MY50G possibly originated from artefact growth, while DG18 was hosting common indoor species from airborne dust.If MY50G were not included, the xerophilic species would not have been detected.The unusual growth conditions affect culture-depending detection, which may explain the lack of studies on the presence of xerophilic fungi in museums.Perhaps these fungi are more frequent in museums than the literature indicates.
As xerophilic fungal growth in museums is not well researched, the risk is not included in the preventive conservation framework underlying the environmental guidelines for museums.Stevenson, 2017 showed that the growth limit of A. penicilloides, detected in Anchers House, was aw 0.585, corresponding to RH 58.5% challenging the guidelines.However, preventing fungal species able to grow at RH 58% in historic houses is neither sustainable nor possible.In these buildings, integrated pest management, including frequent monitoring, air circulation and cleaning, should also act as prevention.
The xerophilic fungal growth in Anchers House challenges heritage preservation and human health.How harmful the fungi are, is difficult to assess, as there is no current data on their degradative properties to materials and no risk evaluation of human exposure.However, knowing the risk is essential, as the value of a museum collection is substantially reduced if it poses a hazard.

Conclusion
This study showed the growth of the xerophilic fungi A. halophilicus, A. penicilloides, and A. magnivesiculatus in Anchers House, challenging heritage preservation and human health.The growth is hard to prevent because the fungi can grow at low RH, and the building is listed with restrictions obstructing climate control.There are limited studies of xerophilic fungi in museums, their growth conditions, hazards to cultural heritage or health, and whether they originate from outdoor or indoor environments.The lack of research complicates preventive solutions, ensuring museum core activities: preservation of cultural heritage and accessibility for exhibition, research, and education.Since this study, Anchers House has recovered from the fungal colonisation and is working towards improvement of the indoor environment.The authors from The Danish National Research Centre for the Working Environment have been granted funding for a research project focusing on preventing xerophilic fungi in museums.

Figure 1 .
Figure1.Anchers House is a historic house museum.Despite minor leaks in the building envelope, there was no discolouration from intruding moisture.The fungal growth on the museum artefact appeared as white and hyaline colonies in the microscope, producing both conidiophores and ascomata.