Biodeterioration of ancient stone materials from the Persepolis monuments (Iran)

The problem of deterioration of art works is particularly relevant in countries like Iran that are rich in cultural heritage. According to UNESCO data, Iran holds the tenth rank in a list of countries possessing the highest number of monuments belonging to the world cultural heritage. Archaeological areas, buildings, mosques, statues, museums and objects are all exposed to different biogenic and abiogenic stresses under generally aggressive climatic conditions. Lichens and fungi are known to actively decompose stone surfaces. This process is both physical and chemical in nature and often reaches deep below the stone surfaces. This is caused by chemical and physical interactions of the microbiota with the fluctuating and often drastically changing environmental conditions. Here, we describe and analyze the mainly physical degradation by invading fungal hyphae between stone crystals and a generally destabilizing stone texture. In addition to physical deterioration, organic acids produced by lichens enhance the chemical decomposing processes. In this work, penetration of hyphal bundles as well as individual fungi was studied, and the biodeteriorating patterns were documented and compared to general physical-chemical weathering phenomena. Several strains of aggressive black yeast-like fungi and bacteria were isolated and cultivated and will be described in a taxonomical context with many other isolates from different localities using physiological, morphological and molecular data.