Invitation to the Defense of Laura Rabbachin

The Examination Panel is made up of: Carolin Bohlmann (chair), Katja Sterflinger (supervisor), and Sergio Enrico Favero-Longo (external appraiser, University of Turin).

Abstract

Petroglyphs exist all over the world and are one of the earliest forms of human expression, offering insights into beliefs, daily life, and cultural identities of past societies. However, as any other natural stone surface exposed to the atmosphere, they are susceptible to physical, chemical and biological weathering processes. Despite their cultural value, scientific research on rock art degradation, and particularly biodeterioration, remains limited. Hence, this thesis explores the role of microorganisms in the deterioration processes of petroglyphs sites in two different climatic regions – the Negev desert of Israel and the alpine region of Austria (Dachstein area) - with the hypothesis that local climatic variables would significantly influence the microbial degradation of the rock surfaces.

A multi-analytical approach was employed to investigate the composition of the lithobiontic communities, their spatial organization, and their interactions with the lithic substrate. Physico-chemical methods were used to determine the composition of the stone (limestone) and of the dark crust (clay minerals with Mn and Fe oxides) covering the desert rocks. Metagenomic analysis combined with microscopy techniques revealed an endolithic colonization of the desert rocks, clearly dominated by bacterial taxa, in particular Actinobacteria and Cyanobacteria, whereas the alpine samples showed an extensive epilithic and endolithic colonization, with more complex microbial communities composed of Bacteria, Archaea, and Eukaryotes. Further microscopic techniques applied on the alpine samples highlighted a general biodeterioration state of the stone and the great boring ability of the biofilms, especially of those with filamentous cyanobacteria (e.g., Nostocales and Oscillatoriales), and showed that a thick moss biofilm (with high abundance of Bacteroidetes taxa) was the most harmful for the stone substrate, causing severe disruption of the underlying rock. The analysis of stone without visible biofilm revealed a microbiome dominated by ammonia-oxidizing archaea, probably indicating the presence of a previous degraded biofilm (source of ammonia), and a current state of deterioration (dissolution of calcium carbonate). In the desert samples, SEM-EDX analyses further revealed deterioration patterns, possibly associated to the activity of biodeteriorative microorganisms that leach the calcareous matrix from the bedrock and mobilize metal cations from the black varnish for metabolic processes, slowly weathering it. To evaluate the potential of these microorganisms to degrade limestone, a cultivation-dependent strategy combined with metabolic assays and weathering tests on limestone slabs was adopted. Results showed that the isolated strains from the Negev petroglyph sites, related to cyanobacteria and heterotrophic bacteria, have the ability to dissolve calcium carbonate. Analysis of the fungal communities indicated, instead, that, although the presence of these organisms as rock inhabitants is scarce, they consist of rock-specialized species such as microcolonial fungi and lichens with high biodeteriorative potential. A final evaluation and comparison of the effects of the lithobionts on the studied petroglyph sites was made, keeping in mind that in environments with high levels of abiotic stress biofilms can also have a bioprotective effect.

Short biography

Laura Rabbachin holds a Master's degree in Chemical Sciences for Conservation and Restoration from Ca' Foscari University of Venice, Italy. Since 2019, she has been part of the Institute of Natural Sciences and Technology in the Arts (INTK) at the Academy of Fine Arts in Vienna. From 2019 to 2021, she contributed to different projects on art materials and their ageing processes, while since 2021, she has been a doctoral student and lecturer. Her doctoral research focused on the biodeterioration of stone cultural heritage in Austria and Israel. From 2025, she will be a postdoc investigating biopatinas on urban architectural surfaces as potential biofilters and bioremediation systems as part of a WWTF-funded project.

The thesis defense will be in English and will take place at the Academy at Augasse 2-6, room D 1.17.15 as well as online via Zoom.

Zoom-Link: https://akbild-ac-at.zoom.us/j/68456510029?pwd=gmTStt4Mo8cVtZu4K2UJlDkSOERQZm.1

We are looking forward to welcoming you.