## 4 Discussion
These microorganisms can cause the dissolution of cations and chelation of metal ions from mortar and mineral pigments, leading to the formation of stable metal complexes whose crystallization results in an increase in internal pressure, resulting in cracking, peeling and the eventual loss of mural fragments [49]. _Aspergillus_ sp. S1 is a suitable example. The finding that some strains increased the pH of the medium could have been a result of the production of alkaline metabolites, such as NH\({}_{3}\) and polypeptides. According to [PERSON] et al. [49], acids are dangerous metabolites, but deterioration can also occur via alkaline reactions through degradation of different nitrogen components or Na salts in organic acids. Our results showed that the tested fungi had both the ability to produce organic acids and significant hydrolytic capacities, indicating their capacity to decompose the tested consolidants and other deposits of organic material on the pictorial layer. All of these activities were expressed in structural and aesthetic alterations in the mural paintings [21]. These broad enzymatic activities allow fungi to grow on every type of material or anywhere they find organic matter [68; 73; 74]. Protcolytic activity suggests the potential of proteases to degrade casein in amino acids, which is needed for colony growth and production of metabolites [69; 75; 76]. _Bipolaris_ sp. M4 and _Ulocadium_ sp. H1 are good producers of proteases and, therefore, considered as two of the primary degraders of TDC. Lipases and esterases are involved in the removal of layers of aged Paraloid(r) B72 [77]. Since the optimum pH for their activity is 8.0 [16], we deduced that, as a first step, the isolates change the substrate pH and then produce hydrolytic enzymes, which show high activity at this pH value. Synthetic resins applied to the monuments result in advanced chemical and physical degradation, such as yellowing and cracking, after about 30 years, facilitating biological degradation [42; 78]. Our results confirmed this hypothesis. All the fungal strains except _Bipolaris_ sp. M4 could colonize both the control and painted experimental models covered with Paraloid(r) B72 and TDC because of their versatile metabolism and their ability to grow on substrates with low nutrient content. The pigments from the painted experimental models most likely contained growth inhibitors, but the consolidants removed this effect because they blocked the direct contact with the spores and mycelium. The investigated fungal species were demonstrated to have the potential to decompose the consolidants used during previous restorations, resulted in the loss of their role fixing the pictorial layer and implicitly rendering them powdery. The use of rapid biodegradation screening tests is mandatory for the assessment of the physiological capacity of autochthonous microbiota (contaminated areas and air spores), which are causative agents of structural and aesthetic weathering. Our results showed that black fungi could colonize not only aged synthetic acrylics but also those that had been recently applied. In situ, the decomposition of consolidants and the biodeterioration of the pictorial layer can be avoided through strict control of the temperature and RH of the microclimate of the indoor environment, thus enabling long-term conservation of wall paintings [79]. Removal of surface adherences from mural paintings is expected to yield colour changes, which is usually an indicator of the efficiency of the removal process [51]. From the colorimetric point of view, there were indeed changes observed for all treated areas, for both the TDC- and Paraloid(r) B72-covered samples. The fact that several fungi yielded the greatest and smallest differences for different pigments might suggest that fungi efficiency in the decomposition of aged consolidants also depends on the interaction of the consolidant with the painted layer. The fact that the removal efficiency values were mostly highly negative can be correlated with the input from the black melanic pigment.