# Role of Exposure on the Microbial Consortium on Historical Rural Granite Buildings
## 3 Results and Discussion
### Next Generation Sequencing
In the Dothideomycetes class, the order Capnoidales occurred on N- and W-facing walls of all churches. _Catenulostroma protearum_ occurred on the N-facing walls of all three churches (19, 3, 24% in SMV, BAR and ROC respectively) and on the W-facing wall of the ROC church (7%). _Nevoderiesia lagerstroemiae_ colonized both N-and W-facing walls of the SMV church (1 and 10.5%) and _Deuriesia streltiziiicola_ colonized the N-facing walls of the SMV and BAR churches (1.8 and 5.6%). Within the class Eurotiomycetes, the most widely represented order is Chaetothyriales. Within this order, species from the family _Herptrichielaceae_ were found to colonize the N- (12.6%) and W- (1.2%) facing walls of the SMV church and the N-facing wall of the BAR church (11%); species of _Rhinocdiaella_ colonized the N-facing wall of the SMV church (14.6%) and the W-facing walls of all three churches (3, 15 and 1%); species of _Knufia_ colonized the W-facing wall of the SMV (10%) and ROC (2%) churches and species of the genus Cladophialophora colonized the N-facing wall of the BAR church (5.6%). The presence of species of the genera _Catenulostroma, Rhinocdiaella_, and _Kunfia_ (_Contiosporium sp. MA 4597_) have previously been found to be linked to biodeterioration processes on stone monument facades [74], and its EPS linked with process of corrosion [75]. In fact the vast majority of rock-inhabiting fungi have the ability to penetrate intercrystalline, producing small holes (biopitting) or taking advantage of previous fissures [76, 77, 78]. They are also considered to be one of the most stress-tolerant eukaryotes known, in part due to EPS production and their thick cell walls [79]. It is also important to note the absence of ubiquitous genera such as _Aspergillus_, _Cladosporium, Penicillin_, or _Alternaria_, all of them widely described as members of the microbiome of monuments [80, 81]. However, in the case of _Alternaria_, it is a genus more closely linked to Mediterranean environments, and its low presence has previously been reported for the northwestern part of the Iberian Peninsula [82], where the studied churches are located. In addition, _Aspergillus_ and _Penicillium_ spores have been reported to be more frequent in urban than in rural areas [83], such as the one in the study. In relation to the phylum Basidiomycota, a low presence was detected on the ROC church. However, species of the _Rhinocchia_ genus (Agaricomycetes) were identified on N-and W-facing walls of the BAR church (7.3 and 1.6%) and on the N-facing wall of the SMV church (4.2%), and species of _Fellowces_ (Tremellomycetes) were found on the N- and W-facing walls of the SMV church (2%). The presence of lichenized fungi and non-lichenized fungi must be taken into account in evaluating biodeterioration as several lichenized and non-lichenized fungi secrete a variety of acidic primary and secondary metabolites with chelating functions, thus affecting the integrity of the stone [16]. Excreted acids react with different ions in the substrate, leading to biocorrosion and formation of secondary myogenic minerals [84]. Lichens mainly cause physical weathering of granitic rocks, by inducing disaggregation of surface grains and engulfing them in their thalli [8, 9]. The chemical action of the lichens on the granite causes dissolution of the minerals by production of organic acids as well as by an increase in the time of contact between the rock and the attacking solution [7]. On the other hand, black fungi are known to possess thick walls and produce significant amounts of EPS as a method to reduce environmental stress. EPS production allows these organisms to survive extreme conditions, such as temperature fluctuations, water stress, UV radiation, or nutrient deficiency [85]; however, it leads to the deterioration of stone [86]. Thus, taking into consideration the organisms found on the three churches, although the total microbial diversity did not depend on the different locations, it did depend on the orientation of the walls and was highest on the N-facing walls.