HIDDEN IN THE COAT: GEOMICROBIOLOGICAL INVESTIGATIONS OF ROCK ART ECOSYSTEMS AND CHALLENGES FOR THEIR SUSTAINABLE PRESERVATION

Rock art is a precious heritage that prevailed from prehistory into the modern times, it holds significant implications to past cultures and climate changes and are found in most of the world. It indicates the development of human cognition and modern behavior, while recording the fauna and flora that were long gone due to shifting landscape and climate. Rock art is also increasingly fragile, under the threats of human development, vandalism, looting, inadequate tourist management and natural weathering. It is fundamental to understand how rock art was made and its state of preservation before we can proceed with any preservation issues. Technical analysis of pigments and ochre investigate ancient technologies and provides clues for the manufacture of rock art that could also relate to the cultural choices and available resources of the people that made them. Major processes affecting rock art sites include natural and human influences. To understand the above, inorganic and organic components could be identified by a variety of analytical instruments, but concerning the long-term preservation of rock art, non-invasive or micro-invasive investigations have priority over invasive sampling that will result in ultimate loss. Because rock art is a fragile heritage of high value, we proposed a sustainable approach toward its analysis and preservation that will minimize sampling, but at the same time acquire important information about technology and weathering state. In Oman we sampled rock varnish adjacent to petroglyphs on the same boulder, and obtained weathering, microbial activity and radiocarbon dating information that gave us a limit ante quem for the making of engravings to establish a proposed chronology of past events, meanwhile keeping the petroglyphs unharmed. Weathering of the rock surface involves complex interactions between minerals and microorganisms, in which the contribution of microbes to rock surface decay has long been noticed. Biotic weathering caused by lichen and other biological organisms on rock art and stone materials is well known in literature and involves the dissolution of the substrate and precipitation of new minerals formed by producing acids such as oxalic acid and carbonic acids. But in some cases microorganisms are suggested as beneficial to rock preservation. Biological organisms can hold fragile rock surfaces in place and produce protective rock coatings of oxalic crusts. Microorganisms are associated with the biomineralization of biological rock coatings, for example oxalate crusts are often formed by lichens and fungi. Research in rock coatings is important to the preservation of rock art, and microorganisms play an important role in changing both the composition and color of rock art surfaces. We visualized the biofilm structure and extracted genomic material on rock art samples with different colored coatings from Ethiopia, then identified bacterial communities by amplifying and sequencing the 16S rRNA gene. Bacteria with mineralization potentials that could form patinas were identified, as well as animal microbiome that could result from herding activities at the site. The results imply that different colored coatings from the same rock art panel could harbor microbial communities with different compositions and functions. Cultural heritage made of stone is often discolored by pigments from biofilms, therefore a review was made to discuss microorganism-produced pigments concerning their role in the broader ecological context, and the possibility of using microbial pigments as an indicator of microbial impact on stone. The formation of rock coatings is a complicated issue that needs expertise in both geology and biology, therefore we combined interdisciplinary methods in geochemistry, molecular biology and bioinformatics to further understand how microbial communities are involved in the formation of rock art coatings. In the last part of this thesis we present a paper that utilized cross-disciplinary scientific methods to understand bacterial communities on rock coatings from rock art, and reveal new insights into bacterial diversity and functions related to the formation of rock coatings.