Biotic and abiotic factors involved in the white alteration on frescoes developed inside the Ubisa Monastery Church (Ubisa, Georgia)

White alterations on historical painted walls are often induced by water infiltration phenomena, with serious conservation implications such as the obscuring of readability and the loss of painted layer. The Church of the Ubisa Monastery (Georgia), an active religious site, exhibits a peculiar location with cold winters and hot summers and a complex micro-environmental situation. A whitish veil-like alteration was observed on the XIV century byzantine frescoes of this church since 2018, widely covering the walls of the main nave even in 2024. Different on-site (bioluminescence) and laboratory analysis (cultural-dependent and cultural-independent biological investigations, XRD, FT-IR and ionic chromatography) were conducted for determining the etiology of this alteration. Halophilic bacteria ( Halococcus sp., Rubrobacter bracarensis ), airborne and soilborne fungi ( Aspergillus, Penicillium, Trichoderma, Cladosporium , Alternaria ), some plant pathogens and saprophytes ( Ralstonia, Biscogniauxia, Rhizosphaera, Vararia, Peniophora ) and human-related microbes ( Malassezia , Staphylococcus ) were identified. Moreover, salts such as gypsum, calcite, sulphates, potassium nitrate and chlorides were evidenced. Both microbial biodiversity and the presence of salts were related to the surrounding environment in which the abbey is situated. Such numerous plant pathogens are indicated for the first time inside of a heritage monument. The results will support an integrated plan management for the conservation of this important site considering its geomorphologic and anthropic aspects.