## 4 Discussion
### Potential Bioderiorative Effect  
The possible implications of the detected microbial communities on substrate deterioration deserve careful consideration. Initially, discoloration is observed, manifesting as white, yellow, and pink hues, accompanied by the formation of an exopolysaccharideacharide (EPS) matrix corresponding to the dark green and hard black alteration phenomena. _R. tropici_ is particularly known for its substantial EPS production; however, several aspects of this organism's growth and EPS production remain inadequately characterized, particularly about the influence of environmental factors on EPS synthesis [88]. Similarly, _M. yumannensis, M. aloeverae, P. megaterium, M. flavescens, A. parietis_, and _N. suwonense_ produce varying amounts of EPS, depending on their specific environmental conditions. In this study, EPS was also detected by Raman spectroscopy (Figure 5B) in correspondence with sample S\({}_{6a}\) (where _R. tropici_ was detected), as well as in samples S\({}_{6a}\) and S\({}_{7}\), further supporting the observed findings. It is well documented that salts present in the substrata, in contact with microorganisms, can enhance EPS production [22]. Additionally, it has been demonstrated that the combination of salts and microorganisms, (e.g., moderately halophilic bacteria) amplifies the deterioration effect, producing a more significant impact than the action of either factor [22]. The detection of EPS is particularly important in the context of conservation treatment, especially in biocide applications. The presence of an EPS matrix can compromise the effectiveness of such treatments [89], highlighting the necessity of considering this factor in conservation strategies. Finally, although _R. tropici_ is a nitrogen-fixing bacterium, it also exhibits carbon metabolism, producing enzymes in free-living cells that oxidize carbon compounds of various origins [90]. Additionally, the Micrococcus genus is known for its proteolytic and fibrotic properties [51], whereas _P. megaterium_ has been isolated from loamy or calcareous soils and described as a carbonatogenic strain capable of precipitating CaCO3[53; 91; 92]. Further investigations are essential to assess the specific chemical or physical deterioration activities arising from their metabolic processes and growth patterns. The current literature provides limited information, primarily focusing on the identification of microbial colonizers rather than their potential role in biodeterioration. Furthermore, Actinobacteria are known to harbor antimicrobial-resistant genes (ARGs) [93], and recent studies have indicated that Actinobacteria and Proteobacteria contribute, on average, to approximately 40% of antimicrobial resistance carrying contigs (ACCs) in stone monuments [94]. Additionally, some bacterial strains exhibit antifungal properties, suggesting that in the context of direct conservation treatments, it is crucial to carefully evaluate the chemical properties of biocides and the spectrum of efficacy against the selected microbial communities. This approach will help mitigate the risk of selecting resistant bacterial strains or encouraging fungal spread [28; 82]. However, it is important asses that in recent years, halophilic microorganisms and their salt-tolerant enzymes have demonstrated considerable potential in the conservation and restoration of cultural heritage, especially for cleaning mural paintings and other stone artworks. In this regard, a system utilizing microorganisms or biocatalysts that can operate across a broad spectrum of salinities may provide an ideal solution for removing unwanted inorganic or organic materials from the surfaces of historical monuments and wall paintings [95]. Moreover, EPS can enable biofilm cells to withstand higher concentrations of biocides. The EPS matrix hinders or blocks biocides from reaching the target microorganisms within the biofilm by limiting diffusion and/or through chemical interactions with the EPS components.