The rapid increase in the antibiotic resistance of microorganisms, capable of causing diseases in humans as destroying cultural heritage sites, is a great challenge for modern science. In this regard, it is necessary to develop fundamentally novel and highly active compounds. In this study, a series of N⁴-alkylcytidines, including 5- and 6-methylcytidine derivatives, with extended alkyl substituents, were obtained in order to develop a new generation of antibacterial and antifungal biocides based on nucleoside derivatives. It has been shown that N⁴-alkyl 5- or 6-methylcytidines effectively inhibit the growth of molds, isolated from the paintings in the halls of the Ancient Russian Paintings of the State Tretyakov Gallery, Russia, Moscow. The novel compounds showed activity similar to antiseptics commonly used to protect works of art, such as benzalkonium chloride, to which a number of microorganisms have acquired resistance. It was also shown that the activity of N⁴-alkylcytidines is comparable to that of some antibiotics used in medicine to fight Gram-positive bacteria, including resistant strains of Staphylococcus aureus and Mycobacterium smegmatis. N⁴-dodecyl-5- and 6-methylcytidines turned out to be the best. This compound seems promising for expanding the palette of antiseptics used in painting, since quite often the destruction of painting materials is caused by joint fungi and bacteria infection.

Microorganisms are a significant cause of damage to cultural heritage, including paintings. Currently, the palette of antiseptics that are used in painting has narrowed considerably. This is due to the increased demands placed on such substances. It was shown that low molecular weight chitosan (LMWC) obtained from the king crab (Paralithodes camtschaticus) exhibits high activity against dominant fungi-destructors of paintings in the State Tretyakov Gallery. Nevertheless, the increasing market demand for chitosan has prompted the exploration of alternative sources. Insects, notably the bioconverter black soldier fly (Hermetia illucens), stand out as one of the most cultivated options. This study investigates the effectiveness of chitosan, isolated from H. illucens by a novel method developed by authors, in inhibiting fungi that damage tempera paintings. The activity of 33 and 39 kDa chitosans from H. illucens is comparable to the most active chitosans previously studied from P. camtschaticus. However, there are characteristic differences between these compounds, as shown by the results of FTIR spectroscopy, which may affect their consumer properties when used in paint materials. Our studies suggest that LMWC from H. illucens is a promising material that can expand the range of antiseptics used in painting. Graphical Abstract

Various heritage objects can be subjected to various types of biodegradation and biodeterioration. Mold fungi can destroy many types of art—be it monumental art or easel paintings. Tempera paintings on wood are at risk of biodeterioration, since the wide variety of organic and inorganic materials in art objects often provide an optimal habitat for biological colonization, causing aesthetic and structural damage. In this regard, timely identification and characterization of their microbiological destructive potential are critical. The fungi Syncephalastrum sp. STG-160 and Cladosporium sphaerospermum STG-161, isolated from bio-lesion sites of the 16th century icon “Descent into Hell” from State Tretyakov Gallery, Moscow, were identified and characterized morphologically and molecularly in our work. Syncephalastrum sp. was found in an unusual habitat that has not been previously described for this species. To determine the biodegradability of the identified fungi, their cells were inoculated onto mock layers—egg yolk ochre, cobalt green tempera pigments, and watercolor black. The results show that some pigments were more degradable than others. The addition of cobalt green completely inhibited STG-161 growth and significantly deceleratedSTG-160 mycelium development, most likely due to the presence of heavy metal ions in the pigment. Ochre, a frequently used pigment in restoration practice, is the most degradable material for Syncephalastrum sp. STG-160. Combining culture-dependent methods with SEM and fluorescence microscopy allowed us to identify an invisible individual spore of Syncephalastrum sp. STG-160 and a single hypha of Cladosporium sphaerospermum STG-161 directly on the icon’s surface in clean-contaminated zones, potentially allowing their development in cases of adverse temperature and humidity conditions. Therefore, in order to ensure rapid and effective conservation, it is crucial to assess and quantify the presence of biological systems causing damage to the heritage object itself as well as its individual art components.

In current work, we for the first time studied the antimicrobial activity of representatives of mold fungi, which occupy a rather specific ecological niche, since they are destructors of tempera painting materials. We screened 24 molds that had previously been isolated from exhibits and in the halls of the State Tretyakov Gallery and for which the ability to destroy materials used in tempera painting and scientific restoration was shown. Screening for antimicrobial activity was carried out against a panel of 16 test cultures, characteristic for identifying activities of various types. The strains exhibited activity, including against Staphylococcus aureus INA 00761 (MRSA), S. aureus FDA 209P (MSSA), Pseudomonas aeruginosa ATCC 27853, Mycobacterium smegmatis VKPM Ac-1339, M. smegmatis mc² 155 and Leuconostoc mesenteroides VKPM B-4177. Among the studied paint-degrading fungi, strains Simplicillium lamellicola STG-96, Cerarobasidium sp. STG-324, Penicillium sp. STG-327 and Penicillium sp. STG-344 turned out to be the most promising for further research related to the determination what specific highly active compounds they produce.

Secondary metabolites, some of which have antimicrobial activity, are a key tool that helps filamentous fungi to occupy a wide variety of ecological niches. In particular, some of these microorganisms are capable of growing on painting materials, which leads to their deterioration. However, this natural reservoir has not been screened for antimicrobial compounds. In the current work, we studied the activity of fungi-destructors of tempera painting isolated in the State Tretyakov Gallery from: the Orthodox icon “Prophet Solomon” of the 18th century—Penicillium chrysogenum STG-117; the Old Russian icon of Sergiev Posadsky school dating to the 15th century—Penicillium rubens STG-305, Penicillium sp. STG-333, P. chrysogenum STG-344, Aspergillus fumigatus STG-345, Penicillium sp. STG-348; and from the Old Believer icon “Descent into Hell” of the 16th century—Syncephalastrum sp. STG-160, Cladosporium sphaerospermum STG-161. The strain Simplicillium lamellicola STG-96 was isolated in Hall 61 of the State Tretyakov Gallery. Optimization of cultivation conditions was carried out for the three strains, STG-96, STG-117 and STG-344, that demonstrated promising antimicrobial activity against panel of representative test cultures on two nutrient media—Czapek-Dox and #2 Gause, with different pH values, in the range of 5.0–10.0. The highest antimicrobial activity was observed at the second and third week of culturing. The antimicrobial activity was also tested for novel isolates: STG-160, STG-161, STG-305, STG-333, STG-345 and STG-348. Strains from the Aspergillaceae family showed high activity against such representative test cultures as methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Mycobacterium smegmatis. Our work demonstrates that fungi-destructors of tempera painting are promising producers of antimicrobial compounds.

The search for new antibiotics that overcome the resistance of pathogenic microorganisms is one of the greatest global challenges in medicine. A key stage in this search is the selection of microorganisms that can potentially produce promising antibiotics. The aim of our study was to isolate and characterize microorganisms from the soil of the Putorana Plateau, a region with an extreme climate, where antibiotic activity of microor-ganisms had not been studied. The actinomycetes Nonomuraea ceibae, Streptomyces lutosisoli, S. mirabilis, S. pratensis, S. rhizosphaerihabitans, Streptomyces sp., and the fungi Trichoderma sp., Truncatella angustata, and Umbelopsis isabellina were isolated and identified based on the morphological and genetic characteristics. The antimicrobial activity and antimicrobial spectrum of the isolated strains were studied. The anti-bacterial activity of U. isabellina, the antimycotic activity of S. mirabilis, and the activity of S. rhizosphaerihabitans against the fungi and antibiotic-resistant bacteria included in the World Health Organization list have been recorded for the first time. The three actinomycetes strains were selected for priority chemical study. Our results demonstrate that microorganisms from the extreme climatic zone might be promising antibiotic producers.