When an international team of researchers, curators and bioinformaticians analyzed the drawings of Leonardo da Vinci, they (most likely) didn’t find the DNA of the Renaissance Man, but they did detect some surprising anomalies—namely, a substantial amount of bacteria compared with fungi, as well as insects and their droppings.
While next generation sequencing has been successfully employed in art conversation previously, Guadalupe Pinar and her co-authors opted for third generation sequencing technologies to overcome specific limitations, such as the inability to assess archaea, bacteria and eukarya simultaneously.
Thus, the researchers employed Oxford Technologies’ Nanopore sequencing technology with a whole genome amplification protocol to perform a rapid diagnosis of the biological infection level of seven of da Vinci’s drawings.
“Although molecular techniques are not completely free from bias, the establishment of next- and third-generation sequencing technologies in the field of cultural heritage is providing a powerful DNA-based approach to monitor the preservation status as well as to foresee the risk of deterioration of valuable objects,” the researchers write in their paper, published in Frontiers in Microbiology
Overall, the results show a surprising abundance of bacteria over fungi. Until now, fungi were thought to be the dominant community in paper-supported art and tended to be the main focus of microbial analysis due to their bio-deterioration potential. But here, the research team identified the “true degraders” as members of the phyla proteobacteria, actinobacteria and firmicutes families.
While scanning electron microscopy found microbial evidence of flies and their excrements, the researchers also observed an unexpectedly high amount of human DNA. Although the shelf life for readable DNA is about 1 million years, it’s highly unlikely any contamination can be attributed to da Vinci. Instead, the team hypothesizes it was introduced during restoration work.
Interestingly, both the bacterial and fungal communities found on the art reveled geographical information. For example, the researchers detected specific taxa in drawings stored at the Royal Library of Turin (Turin, Italy) that were not present in the drawings stored at the Corsinian Library in Rome, and vise versa.
“The data generated can provide interesting information that can contribute to surprising insights into the objects being investigated, such as the selection of materials at the time of manufacture and also uncover important information about the object’s history of use,” the authors said. “This information may help to understand many open questions in a variety of fields, as archeology, history, restoration, philology and criminology.”
But most importantly, Pinar said, Nanopore-generated microbiome data can be used to create a “bio-archive” of the drawings, providing a fingerprint for current and future comparisons.
To enable future examination of these drawings as well as other artistic works, the study authors say the next step is to optimize analytical techniques—based on the study of environmental DNA—that allow both conservation of historical data and reuse of samples. The next challenge for the researchers, specifically, is to measure the activity of individual microbial cells present in the drawings.
“There are techniques that have already been consolidated in other fields of biology, such as cytofluorimetric measures and single-cell RNA sequencing, which examines the sequence information of individual cells with optimized NGS technologies, which would allow a better understanding of the function of an individual microorganism in the context of its microenvironment,” they conclude.
Photo: Sampling microbiome from da Vinci's "Studio di panneggio per una figura inginocchiata" (ca. 1475). Credit: Guadalupe Pinar and co-authors