Microbiological
characterization of frescos in four different locations (CollegiodegliAugustali, Casadel ColonnatoTuscanico, Casa delloScheletro and Casadel GranPortale) of excavation sites of Herculaneum was carried out. The use of
infrared thermography allowed detecting 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 and fungi, particularly of spore forming and mould. In
fact, heterotrophic bacteria were prevalent in all wall paintings monitored
(ranging from 18 ± 2 CFU 100 cm-2
to 68 ± 4 CFU 100 cm-2), whereas fungi were also detected but at
lower levels (ranging from 9 ± 2 CFU 100 cm-2 to 45 ± 3 CFU 100 cm-2).
Cultural–based method allow us to identify by 16S and 26S rRNA
partial sequence analysis heterotrophic microorganisms belonging to different
genera of Bacillus and Aspergillus, Penicillium and Fusarium
together with the unusual genera as Microascus and Coprinus. By using this approach, Bacillus-related
species (B. cereus/B. thuringiensis group, B.
simplex/B.muralisgroup, B. megaterium and B. subtilis)
were isolated in all sample points analysed with
the exception of the Casa delloScheletro
in which Micrococcus luteus/Arthrobacter sp.
group and Streptomycesfragilis were found. DGGE analysis of PCR amplified
V3 region of rDNA from DNA directly recovered from
frescos samples, enabled identification of bacterial species not identified using
culturable technology as those closest related to Microbacterium group, often associated with Brevibacterium, Streptomyces
and Stenotrophomonas. Combination of
culture-dependent and independent methods provided better microbiology
characterization of heterotrophic microbiota
present on the surface of ancient frescos of this important archaeological
site.
