Abstract
Seven emblematic Leonardo da Vinci’s drawings were investigated through third generation sequencing technology (Nanopore). In addition, SEM analyses were carried out to acquire photographic documentation and to infer the nature of the micro-objects removed from the surface of the drawings. The Nanopore generated microbiomes can be used as a “bio-archive” of the drawings, offering a kind of fingerprint for current and future biological comparisons. This information might help to create a biological catalog of the drawings (cataloging), a microbiome-fingerprint for each single analyzed drawing, as a reference dataset for future studies (monitoring) and last but not least a bio-archive of the history of each single object (added value). Results showed a relatively high contamination with human DNA and a surprising dominance of bacteria over fungi. However, it was possible to identify typical bacteria of the human microbiome, which are mere contaminants introduced by handling of the drawings as well as other microorganisms that seem to have been introduced through vectors, such as insects and their droppings, visible through the SEM analyses. All drawings showed very specific bio-archives, but a core microbiome of bacteria and fungi that are repeatedly found in this type of material as true degraders were identified, such as members of the phyla Proteobacteria, Actinobacteria, and Firmicutes among bacteria, and fungi belonging to the classes Sordariomycetes and Eurotiomycetes. In addition, some similarities were observed that could be influenced by their geographical location (Rome or Turin), indicating the influence of this factor and denoting the importance of environmental and storage conditions on the specific microbiomes.
Highlights
Our cultural heritage is an asset that we must protect and monitor in order to pass it on to our future generations
We cannot rule out that the abundance of bacteria in the drawings investigated in this study may be due to the source of contamination to which they have been subjected in the recent past, namely human contamination due to restoration works, and with the human skin microbiome, as well as contamination with insect droppings and their gut bacteria
This study shows for the first time the complete microbiomes of some of Leonardo da Vinci’s most emblematic drawings
Summary
Our cultural heritage is an asset that we must protect and monitor in order to pass it on to our future generations. Generation Sequencing (NGS) technologies have evolved incorporating revolutionary improvements to address the complexities of genomes and metagenomes at an unprecedented speed (Goodwin et al, 2016), being well established in the field of cultural heritage These analyses can be performed either by the socalled "shotgun metagenomic approach," by sequencing the entire DNA library representing all the molecular components of a given sample (Teasdale et al, 2017; Piñar et al, 2020b), or by focusing on specific conserved sequences such as ribosomal RNA genes (Marvasi et al, 2019). The fourth study (Piñar et al, 2020a) applied for the first time the Nanopore sequencing technology together with a whole genome amplification (WGA) protocol to perform a rapid diagnosis of the biological infection on objects of art, unifying all the advantages that this new technology can offer for metagenomic analyses starting from very low DNA concentrations and reflecting the real proportions of all domains of life. This study represents one more example of how the Nanopore technology, in this case in combination with microscopy techniques, can be a practical tool for the rapid biological diagnosis and monitoring in priceless objects
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