# Role of Exposure on the Microbial Consortium on Historical Rural Granite Buildings
## 3 Results and Discussion
### Next Generation Sequencing
In relation to the less abundant phyla, Deinococcus-Thermus, which is associated with tolerance to high radiation and desiccation [50], was only represented by one species, _Truepera radiovictrix_, on the W-facing walls of the SMV and BAR churches (2.3 and 2.9%). The phylum Verrucomicrobia was represented by the species _Chthoniobacter flavus_, on both N- and W-facing walls of the BAR and ROC churches (around 1%). However, the phylum Cyanobacteria was very scarce, and the only species identified were _Loriellosis caverniculae_ and _Trichocleus desertorum_, both at abundances of less than 0.5%, on the W-facing wall of the ROC church. In the present study, Cyanobacteria seemed to be rather scarce, in contrast to the results of other studies investigating the diversity of microbial species found in cultural heritage formed by bricks, marbles [48], sandstones [62] and limestones [63], in which cyanobacteria constituted an important fraction of the community. Across Europe, much lower numbers of cyanobacteria are found growing on granite and sandstone than on other types of stone such as marble and limestone [12], which may indicate a preference of these species for alkaline substrates. In this study, the cyanobacteria most frequently detected by NGS was _Loriellosis cavernicola_, which was previously found in caves in Mediterranean environments [64; 65]. The ability of this species to mobilize calcium ions has been previously described [66] and may favor degradation of the substrate. In relation to the Fungi kingdom (Eukaryota), the phyla most represented on the examined walls are the Ascomycota and Basidiomycota. Within the phylum Ascomyc, the most abundant classes were Lecanromycetes, Dothiocyanetes and Euromycetes, and the least abundant, Sordariumcycetes. Lecanromycetes is the main class conforming lichenized fungi. The most abundant species were _Lecanin cytrella_, which was only found on the W-facing walls of the SMV and BAR churches (51.5 and 19.6), _Solicosporum unbrium_, which was found on the N-facing wall of the BAR church and the W-facing wall of the ROC church (16.5 and 45%), and _Hypogymnia metaphysodes_, which only colonized N-facing walls of the SMV and BAR churches (5.8 and 2.49). Other species of this phylum were also found on different walls of different churches, such as _Lecanora dispersa_ (5%), _Lecania erysibe_ (1%), on the W-facing wall of the BAR church, and _Lecanora horiza_ (2.6%) and _Lepra amara_ (5%), on the N-facing wall of the BAR church. Finally, we found a very high percentage of _Caloplaca maritima_ (14.3%) on the W-facing wall of the BAR church. _Hypogymnia metaphysodes_, _Lecanora dipersa_, _Schasporom unbrium_ and _Lepra amara_ have previously been found on stone monuments [45; 67; 68]: _Lecanora dispersa_ and _Lepra amara_ are included among the main lichens known to colonize Galician granite [9; 45] and have been associated with acidic substrates and cold and humid climates [69]. However, the usual habitat of _Lecania cyrtella_, which is commonly present on the walls of these churches, is wood, and proliferation of this species may be influenced by the presence of surrounding vegetation. Comparison of the effect of the orientation showed that Lecanromycetes was less abundant on N-facing walls than on W-facing walls. This may be due to the fact that some lichenized fungi have a great capacity to withstand very exposed conditions [70], which may lead to successful colonization of walls that are particularly exposed to solar radiation, unlike the N-facing walls, which are always more humid and shaded. In fact, biofilms samples were taken from N- and W- facing walls of these churches, because the south- and east- facing walls, which are more exposed to solar radiation, were completely covered by lichens. The main classes of fungi conforming the 'black fungi' identified in this study were the Dothideomycetes and Eurotiomycetes, which is consistent with the findings of previous studies [71, 72, 73].