Biodeterioration agents dwelling in or on the wall paintings of the Holy Saviour’s cave (Vallerano, Italy)

The preservation of the wall paintings in rural habitats may be difficult because of severe damage caused by living organisms that may discolor and degrade substrata as a consequence of their growth and metabolic activity. In order to set proper protocols for conservative interventions, biodeterioration agents dwelling within the wall paintings of the Holy Saviour’s Cave, in Vallerano, Italy, were analyzed, taking into account their impact on the substrate and their relation with environmental factors. Pigments, binders, and deterioration products of the paintings were examined by spectroscopic and micro-stratigraphic analysis. A predominant whitish grey crust was due to the massive development of the lichen Dirina massiliensis f. sorediata, but Caloplaca xantholyta and Lepraria sp. were also observed, while a brilliant green patina, red powdery granules, and a black biofilm were due to the presence of green algae (Stichococcus sp., Trentepohlia sp.) and cyanobacteria (Chroococcus sp., Nostoc sp.). Black fungi, here analyzed by ITS rDNA sequencing, were also present.