ИСТИНА

Colonization of stone building materials by micromycetes have received a lot of attention in recent years, as fungi are shown to play one of the leading roles in their deterioration (Warscheid, Braams, 2000). The aim of our work was to characterize the fungal complex of stone building materials, i.e. limestone and plaster, in interiors of cultural heritage, to make a distinction of the development of fungal species in the studied materials and to reveal physiological characters, i.e. pH preferences and organic acids production, of actively developing fungal species. For this purpose, samples of limestone and plaster were taken from the interior walls and columns of 14 objects of cultural heritage located in Russian cities and villages. Altogether 117 samples were analyzed. Two agar media, Czapek and Starch Czapek, were used for isolation of fungi. Isolated strains were characterized by morphological and molecular data, that is, by sequencing the ITS and LSU rDNA regions. Fungal development in studied materials was estimated primarily by abundance of isolated species and in addition by their frequency of occurrence. To elucidate the pH growth optimum of the strains MYA-based media buffered at five pH levels, i.e. 4, 5, 7, 9 and 10 were used (Grum-Grzhimaylo et al., 2016). For carbonate dissolution test, CaCO3 glucose agar was used (Pangallo et al., 2012). In general, species from the isolated fungal complex possess different physiological and ecological characters and realize various life strategies. Indeed, the most abundant (abundance from 29% to 7%) and thus the most actively developing in materials were stress-tolerant microfungi, i.e. Acremonium charticola, A. furcatum, Lecanicillium sp., Parengyodontium album, Purpureocillium lilacinum and Sarocladium kiliense. Counts of these species in the obtained samples were high (104 CFU/g and more). They were all strong alkalitolerants except A. furcatum, which was alkaliphile. We propose that tolerance to osmotic stress and high pH values in conjunction with high enzymatic activities give these fungal species an advantage in developing on limestone and plaster for a long period. In addition, A. charticola and Lecanicillium sp. were able to dissolve CaCO3 and thus were potentially very harmful for materials. Moreover, while actively developing in materials, fungi can deteriorate them mechanically or by means of other mechanisms (Unković et al., 2018). Another group of isolated species included generally plant-associated pathogenic fungi and airborne soil species, i.e. Aspergillus flavus, A. versicolor, Cladosporium langeronii, Fusarium sp., Mortierella alpina, Penicillium chrysogenum, Penicillium sp., Pseudogymnoascus pannorum, Talaromyces funiculosus and Verticillium zaregamsianum. These species were less abundant than that of the previous group (abundance from 4% to 0.2%), their counts in samples were 103 CFU/g and more. According to Dornieden et al. (2000), they are presumably the first inhabitants on surfaces of stone walls. When organic sources are expended, these species disappear, thus, in contrast to the previous group, they cannot stay on mineral substrates for a long period. Nevertheless, the majority of them were alkalitolerant, and P. chrysogenum displayed high calcite solubilization activity. The abundance of remaining species was less than 0.2% and these species were isolated in low amounts (102 CFU/g and less). Seemingly, they have got into samples with surface contamination and didn’t play any role in deterioration process. Our research will be helpful in planning the restauration works.