GEOMYCOLOGICAL ASPECTS OF FRESCOES BIODETERIORATION STUDIED USING SCANNING ELECTRON MICROSCOPY AND ENERGY DISPERSIVE X-RAY SPECTROSCOPY
Gavrilenko M, Fomina M.
D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine,
Department of physiology of industrial microorganisms
The importance of this work is related to the problems of the conservation of national heritage, medieval wall paintings in St. Sophia Cathedral, Kyiv, and creating the scientific basis for combating microbial invasion of the frescoes by studying geoactive microorganisms which are the agents of biodeterioration of mineral substrata of the walls.
The aim of this study was to investigate geomicrobiological peculiarities of the frescoes deterioration in St. Sophia Cathedral by using culture-independent methodical approaches.
Methods: scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).
Results and discussion. Visual inspection of some walls of St. Sophia Cathedral revealed numerous sites of deterioration in the form of dark spots of irregular shape ranging in size from 1.5 to 10 mm in some areas with wall paintings and restoration putty. The restoration putty fragments were sampled in the Mikhailovskiy Altar. Carrying out SEM to visualize the alleged microbiological attack on the mineral substrate of the walls in the dark spots areas confirmed that the deterioration of the walls with the paintings is due to the development of microorganisms, namely microscopic mycelial fungi. The obvious signs of the presence of bacteria were not detected. The fungal growth was not observed in the control samples from the undamaged walls without spots. SEM data showed that fungal hyphae in the dark spots were associated with the crystals of the secondary minerals and the numerous clusters of the scaly aggregates precipitated by fungi. It testified that fungi are capable of biomineralization – biogeochemical transformation of the mineral matrix, which can lead to this matrix destruction. EDX analysis showed that the elemental composition of the crystals and scaly precipitates contained chemical elements typical for the mineral matrix of the walls (Ca, C, O, Si and Al), which were apparently transformed by fungi into a soluble form and were re-precipitated on fungal hyphae and in the surrounding microenvironment. According to the EDX data, the large rhomboid-shaped crystals are likely to be calcium malate crystals, which is quite a rare phenomenon under such conditions compared to the common calcium oxalate crystals. However, the precise identification of the secondary mycogenic minerals requires more accurate methods of mineral identification, such as X-ray diffraction technique.
Conclusions. SEM/EDX study showed that the deterioration of the walls in the areas with dark spots is of biological origin and is caused primarily by microscopic mycelial fungi, whose biogeochemical activity leads to the formation of new mineral phases.