## 3 Results and Discussion
### Microbial Risk Assessment at the Museum Palace in Wilanow  
3.1 Bacteria Potentially Involved in the Biodeterioration and Biodegradation of Historical Art Pieces  
Microbial activity plays an important role in the biodeterioration of objects of cultural heritage. This is primarily due to the extraordinary diversity of bacterial metabolism and the involvement of bacteria in biogeochemical processes that affect various surfaces. Lignocellolytic microorganisms, found in most bacterial phyla, are capable of degrading lignocellulosic, which is the main component of paper, plant-based textiles, and wood [38]. Animal-derived materials, such as wool, silk, or hide, are more resistant to degradation, as they are mainly made of keratin, which is a complex of densely packed amino acid chains. However, members of _Alcaligenes_, _Bacillus_, _Proteus_, _Pseudomonas_, and _Streptomyces_ exhibiting keratolytic activity were found to be able to degrade those as well [39]. Successful colonization of historical objects by autotrophic bacteria results in the formation of syntrophic chains, in which one microorganism thrives on the metabolites produced by another species. This phenomenon further accelerates the disruption of a given material by indirect actions, such as acidification or increased water retention [40; 41].  
Previously performed studies highlighted the fact that the biodeterioration mechanisms occurring on historical art pieces, as well as their pace, are determined by the material the object is made of. The Museum Palace in Wilanow hosts a wide range of historical objects made of various materials, including textiles, stone, and wood. Therefore, each object may be subjected to different kinds of deteriorating microbial activity. In this study, we performed a general assessment of the microbial contamination of air at the Museum Palace in Wilanow to recognize the total microbial diversity and how these bacteria may potentially affect historical objects.  
As mentioned above, amongst the identified bacteria, the three dominant taxa were _Bacillus_, _Microoccus_, and _Pseudomonas_. These are heterotrophic bacteria that are often detected as secondary colonizers in biofilms, which are primarily produced by filamentous _Actinobacteria_. Interestingly, such biofilms were found to be responsible for damaging plaster, marble, and textiles [42]. While _Actinobacteria_ build the foundation of these biofilms, by providing simpler organic carbon sources and retaining moisture, secondary colonizers introduce cellulolytic, hemicellulose, and keratolytic activity that further accelerates the biodegradation [42].  
Although the dominant taxa potentially involved in biodegradation were discovered on all tested media, some other bacteria that may also be involved in the destruction of cultural heritage objects were detected exclusively on some media. Examples of such taxa were: (i) _Flavobacterium_, which was previously recognized to be marble degrader [43], was detected only on FA; (ii) members of the _Cytophagales_ order, damaging wooden objects [44], were recovered on FA, R2A, and LB; (iii) _Splingomonas_, recognized as an important biodeterioration agent, previously detected on old manuscripts, wooden sculptures, and mural paintings [45; 46; 47], was found on all media except BHI and YEA. Generally, it was observed that the majority of genera (including _Rhodococcus_, _Achromobacter_, _Oceanobacillus_, _Cellulomonas_, _Arthobacter_, and _Streptomyces_) previously recognized as being involved in the biodeterioration of historical objects was detected only on selected non-rich media. This proves that the rich media commonly used for microbiological contamination assessments in museums generate strongly biased results.