A MICROBIOLOGICAL SURVEY OF THE ETRUSCAN MERCARECCIA TOMB (ITALY): CONTRIBUTION OF MICROORGANISMS TO DETERIORATION AND RESTORATION

The Necropolis of Tarquinia (Italy), included by Unesco in the world heritage since 2004, is notable for the large number of rock-cut tombs which retain on their walls paintings of daily life and of funeral rites and banquets. Solutions for the safeguard of these sites, that represent to some extent an unicum, are linked to the knowledge on colonising microorganisms supported by the peculiar ecological conditions of hypogeum environments. Aim of this work is a microbiological survey of the Etruscan Mercareccia Tomb and the selection of strains suitable for biotechnological application in the field of restoration. The Tarquinia tombs are mostly simple rectangular chambers, while the Mercareccia Tomb has an outer chamber (dromos) with a timber roof sloping to a central opening which reproduces the atrium of a house of the time as described by Vitruvius, so far in a rather poor state of preservation and now under restoration. 142 different heterotrophic colony morphotypes have been isolated, 16% of which result not yet described in relation to artistic heritage. The most represented bacteria belong to Actinomycetales and Bacillales; fungi belong to the taxa Sordariomycetes, Eurotiomycetes, Ascomycota and Dothideomycetes. The presence of unculturable microorganisms has been highlighted by means of t-RFLP analysis. The investigation has subsequently been focused on the selection of two opposite metabolic functions: the biomineralisation (71 strains) and the solubilisation of calcareous patina (only 5 strains). The most efficient strains in biomineralisation of calcium carbonate have been tested in vivo for consolidation experiments of “Pietra di Lecce”, a calcareous stone. The calcite deposition has been monitored by capillary water absorption, colorimetry, biofilm formation (SEM microscopy). The best results have been obtained with the strain TSND13 Rhodoccoccus erythropolis, applied for the first time as agent for biorestoration. TSND13 reduced the water absorption by 20% compared to control, without altering perceptively the original colour of the stone. In order to overcome the problems arising from the use of living cells also the capacity to induce the formation of calcite by cellular fraction (BCF) has been tested in consolidation trials as an alternative technology.