Characterization in the archaeological excavation site of heterotrophic bacteria and fungi of deteriorated wall painting of Herculaneum in Italy.

Abstract

Microbiological characterization of frescos in four different famous locations of excavation sites of Herculaneum (the Collegio degli Augustali, Casa del Colonnato Tuscanico, Casa dello Scheletro and Casa del Gran Portale), were carried out. The use of infrared thermography allowed us to detect sample points on frescos with greatest moisture not visible to the naked eye, resulting in structural damage. The microclimatic conditions provided perfect habitat for bacteria, especially of spore forming and mould. In fact, heterotrophic bacteria were prevalent in all wall paintings monitored, whereas fungi were also detected but at lower levels. Cultural–based methods allowed to obtain a total of 48 bacteria and 23 mould isolates molecularly identified by 16S and 26S rRNA partial sequence analysis. With this approach, Bacillus-related species (B. cereus/B. thuringiensis group, B. simplex/B.muralis group, B. megaterium and B. subtilis) were isolated in all sample points analysed with the exception of the Casa dello Scheletro in which Micrococcus luteus/Arthrobacter sp./Variovorax sp. group and Streptomyces fragilis were found. Mould isolates were closest related to different genera in which predominated Aspergillus, Penicillium and Fusarium together with the unusual genera as Microascus and Coprinus. Sequencing of the 16S ribosomal DNAs, selected on the basis of DGGE profiling, enabled detection of bacterial species closest related to Microbacterium groups in all sample points analysed, also associated with Brevibacterium, Streptomyces and Stenotrophomonas.