The Campania region in southern Italy is noted for its large number of churches that
harbour invaluable frescoes, dated from the beginnings of the 4th up to the 13th
century. The wall paintings represent an integral part of the monuments, and their
deterioration constitutes a potentially significant loss for the world’s cultural
heritage. Heterotrophic microorganisms such as bacteria and mould can grow on the
surface of paintings that contain a wide range of organic and inorganic constituents,
and provide different ecological niches that are exploited by a large variety of
microbial species. We isolated and identified the heterotrophic microorganisms
found in the biodegraded medieval wall paintings of seven historical churches in
Campania. The paintings showed different levels of microbial contamination.
Microbiological analysis of different paintings gave an overview of the different
heterotrophic microorganisms. Bacteria and moulds were isolated from 77% of the
sampling points analysed, in which the most common type of alteration was
discolouration often associated with detachment of the paint layer. Bacterial strains
were identified by 16S rRNA partial sequence analysis. The Bacillus genus was
isolated in all churches, even though the type of species was variable, whereas all
actinomycetes strains, isolated in five of the seven churches analysed, could be
referred to the Streptomyces genus. The similarity of the sequences analysed of the
42 Bacillus spp., 2 Paenibacillus spp. and reference strains of different species
showed that these bacteria differentiated in 14 groups. The most frequentl