RESUMO
A white deposit covering the walls in the Stanza degli Scudi of the Tomba degli Scudi, Tarquinia, Italy, has been investigated. In this chamber, which is still preserved from any kind of intervention such as cleaning and sanitization, ancient Etruscans painted shields to celebrate the military power of the Velcha family. Scanning electron microscopy analysis has revealed the presence of characteristic nanostructures corresponding to a calcite secondary mineral deposit called moonmilk. Analysis of the microbial community identified Proteobacteria, Acidobacteria and Actinobacteria as the most common phyla in strong association with the moonmilk needle fibre calcite and nanofibers of calcium carbonate. Employing classical microbiological analysis, we isolated from moonmilk a Streptomyces strain able to deposit gypsum and calcium carbonate on plates, supporting the hypothesis of an essential contribution of microorganisms to the formation of moonmilk.
Assuntos
Carbonato de Cálcio/química , Cavernas/microbiologia , Acidobacteria/genética , Acidobacteria/isolamento & purificação , Acidobacteria/metabolismo , Actinobacteria/genética , Actinobacteria/isolamento & purificação , Actinobacteria/metabolismo , Carbonato de Cálcio/metabolismo , Itália , Microscopia Eletrônica de Varredura , Proteobactérias/genética , Proteobactérias/isolamento & purificação , Proteobactérias/metabolismo , RNA Ribossômico 16S , Streptomyces/genética , Streptomyces/isolamento & purificação , Streptomyces/metabolismoRESUMO
Mural paintings in the hypogeal environment of the Tomba degli Scudi in Tarquinia, Italy, show a quite dramatic condition: the plaster mortar lost his cohesion and a white layer coating is spread over almost all the wall surfaces. The aim of this research is to verify if the activity of microorganisms could be one of the main causes of deterioration and if the adopted countermeasures (conventional biocide treatments) are sufficient to stop it. A biocide treatment of the whole environment has been carried out before the conservative intervention and the tomb has been closed for one month. When the tomb was opened again, we sampled the microorganisms present on the frescoes and we identified four Bacillus species and one mould survived to the biocide treatment. These organisms are able to produce spores, a highly resistant biological form, which has permitted the survival despite the biocide treatment. We show that these Bacillus strains are able to produce calcium carbonate and could be responsible for the white deposition that was damaging and covering the entire surface of the frescoes. Our results confirm that the sanitation intervention is non always resolutive and could even be deleterious in selecting harmful microbial communities.
