![]() ![]() Similarly, these patinas can be found on stone monuments exposed outdoors Albertano (2012) reports an exhaustive review of the works carried out on this topic. The growth of cyanobacteria on natural rocks leads to variously colored strips, known as Tintenstriche, the composition of which has been widely studied. Their spores, cells, and propagation structures, dispersed by wind, water, and animals (such as birds, bats, and squirrels), adhere to the rock and initiate biofilm formation in which a heterogeneous matrix of microorganisms is held together and tightly bound to underlying surfaces by extracellular polymeric substances (EPS). Phototrophic microorganisms are the first colonizers of rock surfaces in outdoor environments. Black patinas contain microbial communities composed of a wide variety of microorganisms (mainly cyanobacteria, microalgae and rock inhabiting fungi (RIF) ) in different physiological states, that can live as either epiliths on the rock surfaces or as endoliths (cryptoendoliths, chasmoendoliths or euendoliths) within the substrate. The main adaptations are the production of UV-screening compounds, exopolymeric substances that retain an adequate water content, and constituent compounds of thick cell walls that protect cells against physicochemical hazards. Consequently, they can only be colonized by microorganisms characterized by constitutive or fast adaptive cellular or metabolic responses to these conditions. Lapideous artworks can be considered as extreme environments, characterized by inhospitable surfaces exposed to several stresses such as high solar radiation, desiccation and rehydration, considerable diurnal and annual temperature fluctuations, and lack of nutrients. īlack crusts, defined as “crusts developing generally on areas protected against direct rainfall or water runoff in urban environments, composed mainly of particles from the atmosphere trapped in gypsum (CaSO 4.2H 2O)”, are different from black patinas, which are biofilms composed of pigmented microorganisms and represent a very common deterioration phenomenon on lapideous artworks in outdoor environments. The damage is predominantly linked to the production of organic and inorganic acids and to an euendolithic living habitus. The growth of microorganisms (bacteria, cyanobacteria, algae, fungi, and lichens) on lapideous surfaces, as well as aesthetic alteration, can cause an actual deterioration of the stone. Since the late 1990s, this term has also been used to define an aesthetic change of rock surfaces linked to biological colonization. In the field of cultural heritage, the term “patina” has several meanings: the time-dependent darkening of frescos and oil paintings, the superficial oxidation of bronze and copper, and, more generally speaking, the surface transformations that lead to the ageing of artworks. Therefore, the use of NGS to characterize black patinas could be useful in choosing appropriate conservation treatments and in the monitoring of stone colonization after the restoration interventions. Furthermore, the identification of euendolithic microorganisms and weathering agents underlines the biodegradative role of black patina, which has often been underestimated. For the first time high-throughput sequencing allowed the exploration of the expansive diversity of bacteria in black patina, which has so far been overlooked in routine analyses. NGS confirmed the relevance of coccoid and filamentous cyanobacteria observed by optical microscopy and revealed an informative landscape of the fungal community underlining the presence of microcolonial fungi and phylloplane yeasts. Overall, the sequencing highlighted the rich diversity of bacterial and fungal communities and allowed the identification of more than one hundred taxa. This study used Next-Generation Sequencing (NGS) (including shotgun and amplicon sequencing) to characterize the black patina of the travertine embankments ( muraglioni) of the Tiber River in Rome (Italy). Black patinas comprise a wide variety of microorganisms, but the morphological plasticity of most of these microorganisms hinders their identification by optical microscopy. ![]() ![]() wind and temperature changes), represent extreme environments that can only be colonized by highly versatile and adaptable microorganisms. These substrates, exposed to sunlight, and atmospheric and environmental agents (i.e. Black patinas are very common biological deterioration phenomena on lapideous artworks in outdoor environments. ![]()
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |