# Black Fungi on Stone-Built Heritage: Current Knowledge and Future Outlook
## 1 Background  
Stonework, such as artistic sculptures, historical buildings, monuments, archaeological sites, caves, etc., are ubiquitous across the globe, being an expression of culture, religion, aesthetics, and building techniques of populations, typical of certain historical construction periods. Due to their unicity and intrinsic value, ensuring the integrity of stone-built heritage for posteriority is a critical issue. The study of biodeterioration of cultural heritage is a hot topic of broad interest to the researcher's community and the implementation of safeguard measures is one of the main goals. All materials are subjected to a natural weathering, and \"biodeterioration\" of stones should be considered as an integral part of bio-geo-morphogenesis [1, 2, 3, 4]. The term \"biodeterioration\" defines any irreversible transformation of inorganic or organic material with economic, commercial, historic, and artistic loss caused by macro- and micro-organisms [5]. \"Biodeterioration\" is a very complex matter and conservators should also take into account whether the observed biologically driven phenomena can even be considered positive for the artifact. In fact, in some cases, the presence of subaerial biofilm (SABs) may have a protective effect on the surface [6]; on the other hand, SABs developed at the interface between rock surface and air is considered the main cause of biodeterioration of stone monuments [7, 8]. Microbial biodeterioration of stones is often associated with the presence of a complex community formed by chemo-oragonotrophic microorganisms (bacteria and microfungi) and autotrophic microorganisms (such as algae and cyanobacteria and to lesser extentautotrophic bacteria) usually embedded in an extracellular matrix EPS (in which are present DNA, enzymes, pigments, lipids, proteins, etc.). Microbial cells in the EPS show a typical biofilm lifestyle that confers resistance to hostile environments and reinforces the attachment of microorganisms on the surface [6; 9]. The prevalence of one or more group of microorganisms depends on numerous factors which include the intrinsic characteristics of the material (such as lithotype, porosity, roughness, and state of preservation) that affect its \"bioreceptivity\" _sensu_ Guillitte [10]. The species composition can vary greatly depending on climatic and microclimatic conditions such as temperature, solar irradiation, shining, nutrient and water availability, and, last but not least, the characteristics of species involved [6]. However, microbial colonization is a very dynamic process in time and space, that is the result of the interactions between microbial species and substrates. It varies continuously during the year following the seasons, and it is also under the influence of the dispersion ability of propagules in the air [11; 12; 13]. In recent years, much knowledge has been gained about rock-inhibiting black fungi, and important issues concerning their taxonomy, physiology, phylogeny, and weathering processes [14] have been clarified. However, the majority of studies concerned black fungi from natural environments [4; 7; 15]. In the field of cultural heritage, most reviews had as a topic the biodeterioration of stone caused by fungi in general [6; 16; 17]; some have focused on the microbial and fungal deterioration of various type of substrata (both organic and inorganic such as textile, parchment, wood, paper, metals, and stone) used for artworks [18]; few concerned exclusively black fungi as a cause of biodeterioration of stone monuments [19; 20]. This paper aims to give an overview on the present knowledge of rock-inhibiting black fungi in the field of stone cultural heritage with reference to their taxonomy, biodeterioration pattern, methods of study, and control, with a look to a future perspectives.