Role of Fungi in Biodeterioration
Additionally, stone objects may support novel communities of microorganisms that are active in biodeterioration process. This investigation focuses on mycological analyses of microbial biofilm from two important buildings, made of granite and sandstone, and which were heavily colonized by fungi. The 23 fungal taxa including filamentous microfungi and yeasts with specific distribution on sandstone and granite substrate were isolated. Melanized fungi from Dematiaceae (Deuteromycotina) were dominant.
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The identified microfungi cause discoloration, as well as mechanical exfoliation of building stone material that was analyzed through mechanical hyphae penetration and production of dark pigments and organic acids. KEY WORDS: biodegradation, cultural heritage, fungi Numerous factors affect the stone durability. Stone surfaces are continuously exposed to physical, chemical and biological degradation. Physical, chemical, and biological agents act in co-association, ranging from synergistic to antagonistic, to the deterioration.
Among biological agents miroorganisms have critical importance, in stone deterioration. They can cause various damages on the stone surface, such as: formation of biofilm, chemical reactions with substrate, physical penetration into the substrate as well as pigments production. Numerous studies have been dealing with establishing the role of biological agents in the stone deterioration During the recent decades there has been a general concern about the deterioration of historic buildings.
Along with chemical and physical factors, microbial growth plays an important role in this process (S u i h k o et al. , 2007). Microbial colonization of stones depends on environmental factors such as water availability, pH, climatic exposure, nutrient sources, and petrologic 245 parameters such as mineral composition, type of cement, as well as porosity and permeability of rock material (W a r s c h e i d and B r a a m s, 2000). The stone ecosystem is subject to harsh environmental changes, especially temperature and moisture, exerting extreme selective pressure on any developing microbial community (M a y, 2003).
Bioreceptivity of stone depends on its structure and chemical composition, while the intensity of microbial contamination is determined by the climatic conditions and anthropogenic eutrophication of the atmosphere (P r i t o and S i l v a, 2005). Biofilm formation on clean surfaces usually starts with phototrophic organisms (algae, cyanobacteria) which use CO2 from the atmosphere as their carbon source and sunlight as their energy source. Heterotrophic organisms (most bacteria and all fungi) need some organic source for their growth, which is provided by metabolites of phototrophic organisms or by air-borne deposition.
It has been shown that very low nutrient requirements of some rock inhabiting heterotrophic microorganisms may be fulfilled by remains of polluted air and rain or animal remains and secretion (S u i h k o et al. , 2007). The aim of this work was to study the microfungi community on biodeteriorated stone samples originating from two historical buildings by using cultivation and microscope observations in order to evaluate the potential damage caused by fungal species.
Sampling Samples of stone were collected from two localities: “Monument of the Unknown Hero” (Avala Mountain near Belgrade) and “Brankov most” (Sava river, Belgrade), and two types of stone: granite and sandstone. After a careful observation visible alterations and degradation were mapped and after that the samples were taken. Granite and sandstone samples were taken for mycological analyses by swabbing surfaces with sterile cotton swabs. The samples were then stored at 4°C. Cultural media and inoculations Swab samples were diluted in 10 ml sterile distillated water and shaken mechanically for 10 minutes.
Malt-streptomycin-agar (MSA) medium (MA according to B o o t (1971), with 500 mg streptomycin per liter) was inoculated with 1 ml of the resulting suspensions. Each sample was repeated in triplicate. The plates were incubated at 24°C in thermostat. Isolation of the formed colonies was done successively, using standard mycological medium (Malt extract agar, Potato-dextrose agar and Czapek’s solution agar). All the cultures were grown 7 days in thermostat at 24°C. Macroscopic and microscopic characteristics of the obtained isolates were examined.
The mentioned fungal species are typically soil fungi, which is in accordance with the results who noted considerable number of the same genus and species. The identified microfungi cause discoloration, as well as mechanical exfoliation of building stone material that was analyzed through mechanical hyphae penetration and production of different pigments (Aureobasidium, Cladosporium, Alternaria) and organic acids (some species of genus Aspergillus, Alternaria, Penicillium).