## 3 Results  
### Characterization of Biological Colonization  
As summarized in Table 1, the bioluminometric survey revealed varying ranges of ATP values corresponding to the different alteration patterns identified during field observations using the USB-portable microscope (Figure 3). The control sample (Ss), composed of only salt efflorescence with no visible biological colonization, exhibited an ATP value of 97 RLU/cm\({}^{2}\) and was used as the baseline reference. Higher ATP values, starting from 2026 RLU/cm\({}^{2}\), were recorded in samples associated with visible alteration phenomena, including salt efflorescence (S\({}_{2}\), S\({}_{8}\)), pink discoloration (S\({}_{5a}\), S\({}_{6a}\)), light green areas (S\({}_{11}\)), hard black spots (S\({}_{9}\)), and dark green areas (S\({}_{3}\), S\({}_{7}\)). These findings indicate a significant biological colonization linked to the observed alteration patterns. Conversely, moderately elevated ATP values, ranging from 238 to 476 RLU/cm\({}^{2}\), were found in samples S\({}_{4}\) and S\({}_{10}\), suggesting a limited degree of biological activity. The ATP values in sample S\({}_{1}\) were comparable to those in the control (Ss), confirming the absence of detectable biological contamination. Notably, no evident microbial growth was detected in sample S\({}_{5a}\) using culture-based methods, whereas optical microscopy revealed no microbial structures in samples S\({}_{7}\) and S\({}_{9}\). Nevertheless, scanning electron microscopy (SEM) analyses conducted on S\({}_{6a}\), S\({}_{7}\), and S\({}_{9}\) revealed morphological features of extracellular polymeric substances (EPS) on the surface of the samples (Figure 4(a\({}_{1}\),b\({}_{1}\),c\({}_{1}\))), suggesting microbial metabolic activity. However, morphological and molecular analyses of the samples exhibiting the highest ATP values (ranging from 8019 to 30,542 RLU/cm\({}^{2}\)) enabled the identification of a diverse set of microorganisms associated with distinct alteration patterns (Figure 3). These included Fungi (Ascomycota) in S\({}_{2}\) and S\({}_{8}\), Bacteria (Proteobacteria, Actinobacteria, Bacillota and Pseudomonadota) in S\({}_{6a}\), and green algae (Chlorophyta) in S\({}_{11}\) (Table 1). The alteration phenomenon known as \"white turf\" (S\({}_{2}\), S\({}_{8}\)) was found to be caused by an extensive colonization of _Parengyodontium album_, a chemoorganotrophic fungal species that relies on environmental nutrients for its development. This species is ubiquitous and is frequently detected on monuments, such as churches, cathedrals, and monasteries (2014). The formation of a pink patina (S\({}_{4}\), S\({}_{5}\), S\({}_{6}\)) was recognized using the field stereomicroscope. The pink alteration (S\({}_{6a}\)) shows a wide composition of soil bacterial strains, commonly associated with the rhizosphere of higher plants ([PERSON], 1996; [PERSON], 1996; [PERSON], 1996; [PERSON], 1996). Notably, these microorganisms have also been reported on various wall paintings ([PERSON], 1996; [PERSON], 1996; [PERSON], 1996; [PERSON], 1996; [PERSON], 1996). Figure 3: Stereofield images of sampling points. In detail, in S6a isolate number 1, the presence of _Rhizobium tropici_, a nitrogen-fixing Gram-negative bacterium, which can establish symbiosis is here recognized in free-living form [45]. In S6a isolate number 2 _Microococcus yununanensis_ and _M. aloeverae_ species are redlassified as later heterotypic synonyms of _Microococcus luteus_, a Gram-positive coccus that is catalase-positive, oxidase-variable, and strictly aerobic [55], forming yellow colonies with tolerance to NaCl of 6-8% and 5-12% (\(w/v\)), respectively. In S6a isolate number 3, _Pristia megaterium_ strains have a cell width greater than 1 \(\upmu\)m and can undergo sporulation. It is particularly interesting due to its unusual physiology, useful enzymes and products, and its wide range of ecological habitats [56].