The micro-biota of a sub-surface monument the medieval chapel of St. Virgil (Vienna, Austria)

The medieval chapel of St. Virgil is located sub-surface beneath the square of the dome of St. Stephen, in the heart of Vienna. The walls of the chapel are in direct contact with the surrounding soil. The water migrating horizontally into the walls of the chapel carries a huge load of soluble salts which crystallize on the surface of the walls and within the material. This phenomenon is causing material losses and destruction of original medieval fineries and paintings. Moreover, the salt creates special living conditions for microbes growing on and in the walls which is characterized by a high osmotic stress. The diversity of the micro-biota was studied both by cultivation and molecular techniques [a combination of denaturing gradient gel electrophoresis (DGGE) of PCR-amplified DNA encoding 16S rRNA and the construction of clone libraries]. The fungal diversity was found to be relatively low, albeit cell counts show more than 105 colony forming units per gram of wall material. In the contrary, the diversity of bacteria was found to be high (more than 8 different genera). Furthermore, a community of extremely halophilic archaea was detected consisting of different species of two predominant genera, i.e., Halococcus and Halobacterium.