Isolation and identification of fungal biodeteriogens from the wall of a cultural heritage church and potential applicability of antifungal proteins in protection

Abstract

Fungi are able to permanently damage cultural heritage buildings and stone monuments. Protection against these biodeteriogen fungi is challenging because it may require the use of drastic techniques to remove fungal colonies and chemicals, which can cause further damage, especially on mural paintings. Natural biocides are less damaging, greener, and safer and mainly include essential oils and plant-derived substances. Studies on the applicability of purified antifungal proteins in the conservation of cultural heritage buildings are lacking. In this study, we isolated mold mycoflora from the biodeteriorated inner walls of the Calvinist church of Kézdialbis (Kézdialbis, Romania) and investigated the in vitro antifungal efficacy of Neosartorya (Aspergillus) fischeri antifungal proteins, NFAP and NFAP2 against them. Antifungal susceptibility testing revealed that these proteins inhibited the growth of the most commonly isolated indoor biodeteriogen fungi from the site (Aspergillus creber, Aureobasidium pullulans, Cladosporium sp., Penicillium chrysogenum, and Parengyodontium album) and not common ones (Mucor hiemalis, Sarocladium kiliense) with different spectra and efficacies. A phytopathogen and an entomopathogen species (Pseudopithomyces chartarum and Beauveria pseudobassiana, respectively) were also isolated and described first as fungal biodeteriogens of the inner walls. Among them, P. chartarum was susceptible to NFAP2. Next, we tested the applicability of NFAP and NFAP2 in protecting cultural heritage buildings in a wall model experiment against A. creber. Topical application of both antifungal proteins significantly decreased the area infected by fungi. Scanning electron microscopy of the wall models showed that A. creber had reduced growth and conidiation in the presence of NFAP and NFAP2. This inhibitory activity was maintained for a long time. Strong UV irradiation decreased the protective effect of both proteins in the wall model. Taking into account these results, the high stability of NFAP and NFAP2 in harsh environments, and their bulk recombinant producibility, we suggest that both can be used in the protection and posttreatment of painted walls of cultural heritage buildings to clean up mural painting or to inhibit mold recolonization after mechanical, physical, or chemical decontamination.