Portrait of a man in red crayon (1512). “/>Guadalupe Piñar et al.
Microbiomes are all a scientific rage, even in art conservation, where studying the microbial species converging on artworks can lead to new ways to slow the deterioration of priceless obsolete works of art, and potentially unmask fakes. For example, scientists have analyzed the microbes found on seven of Leonardo da Vinci’s drawings, according to a recent paper published in the journal Frontiers in Microbiology. And in March, scientists at the J. Craig Venter Institute (JCVI) collected and analyzed cotton swabs from ancient art in a private collection in Florence, Italy, and published their findings in the journal Microbial Ecology.
The researchers behind the earlier March paper were JCVI geneticists who collaborated with the Leonardo da Vinci DNA project in France. The work built on an earlier study that looked for microbial signatures and possible geographic patterns in hair collected from people in the District of Columbia and San Diego, California. They concluded from that analysis that microbes can be a useful geographic signature.
For the March study, the geneticists at JCVI took microbes swabs from Renaissance-style pieces and confirmed the presence of so-called “oxidase-positive” microbes on painted wood and canvas surfaces. These microbes feast on the compounds found in paint, glue and cellulose (found in paper, canvas and wood) and in turn produce water or hydrogen peroxide as byproducts.
“Such byproducts are likely to affect the presence of mold and the overall rate of deterioration,” the authors noted in their paper. “While previous studies have attempted to characterize the microbial composition associated with the decay of artworks, our results summarize the first large-scale genomics-based study to understand the microbial communities associated with aging artworks.”
As an added bonus, they found that they could distinguish microbial populations on different types of materials. In particular, stone and marble art created more diverse populations than paintings, possibly because of the “porous nature of stone and marble that harbor additional organisms and possibly moisture and nutrients, along with the likelihood of biofilm formation,” they wrote. Oil paintings, on the other hand, provided more lean nutrients for microbes to metabolize.
The authors acknowledged the small sample size, but nevertheless concluded that microbial signatures can be used to differentiate illustrations based on the materials used. As always, more research is needed. “Of particular interest would be the presence and activity of oil-degrading enzymes,” the authors wrote. “Such approaches will lead us to fully understand which organism (s) are responsible for the rapid decay of artworks, while this information may be used to attack these organisms to prevent degradation.”
Renaissance art wipe
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Collage of the various artworks sampled by geneticists from the J. Craig Venter Institute for a March paper. Circles indicate the smoothed areas on each sample artwork
JCVI
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Manolito G. Torralba and colleagues used small, dry polyester cotton swabs to gently collect microbes from ancient Renaissance-style art in the home of a private collector in Florence, Italy.
Jesse Ausubel
Guadalupe Piñar and her team from the University of Natural Resources and Life Sciences in Vienna, Austria, collaborated with curators from the Instituto Centrale per la Patologa degli Archivi e del Libro (ICPAL) for the microbiome analysis of the Leonardo da Vinci drawings. Last year Piñar et al. relied on microbiome analysis to study the storage conditions of three images retrieved from smugglers and to determine their possible geographic origin. Earlier this year, they analyzed the microbiome of 1,000-year-old parchment paper, from which they could deduce the animals whose skins were used to make the parchment paper.
For this latest paper, Piñar’s team turned to a third-generation sequencing method known as Nanopore, which uses protein nanopores embedded in a polymer membrane for sequencing. It comes with a pocket-sized portable sensor device called the MinION, making it ideal for cultural heritage research. For the Leonardo drawings, Piñar et al. combined the Nanopore sequencing with a whole genome amplification protocol.
The ICPAL conservators used a delicate, non-invasive micro aspiration (i.e. filter suction) sampling method to collect dust particles, microbial cells and other debris from small areas on both the Straight ahead and to of each drawing. Then the DNA was extracted, amplified and sequenced. The Austrian team used optical microscopy to image interesting features in all seven drawings and scanning electron microscopy (SEM) to analyze all the microobjects collected from the drawings.
A “biological family tree”
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Leonardo da Vinci’s drawings analyzed in a study of Austrian and Italian scientists.
Guadalupe Piñar et al.
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Leonardo da Vinci’s sampling microbiome Curtain study for a kneeling figure (c. 1475)
Guadalupe Piñar et al.
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Leonardo da Vinci’s Man of the Bitta.
Guadalupe Piñar et al.
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Insect droppings appear as waxy brown deposits on the fibers of drawing L4 (Studies of a horse’s front legs).
Guadalupe Piñar et al.
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SEM images of the surface of a membrane used to draw the surface of the L3 drawing (Nudes before the battle of Anghiari).
Guadalupe Piñar et al.
Each drawing had its own unique microbiome – an “independent molecular profile or biological family tree.” But Piñar et al. were surprised to find that bacteria generally dominated fungi in the microbiomes of the drawings, contradicting the widespread belief that fungi would be more dominant, given their greater potential to colonize on works on paper. The researchers discovered no visible biological deterioration on the drawing, except for rust spots (small yellow-brown spots or flecks).
Many of those bacteria are mostly found in human microbiomes, suggesting that they made their way into the drawings during the restoration, although you could speculate if it came from the artist himself. (The authors note that bacteria in dust can “stay in suspension” for a long time.) Other bacteria were typical of insect microbiomes and may have been introduced long ago by flies that deposit feces on the drawings. Those feces showed up on image analysis as waxy brown deposits in the fibers.
The Austrian / Italian team could not definitively conclude whether any of the microbial contaminants date back to Leonardo’s time. It seems much more likely that the human microbial elements are the result of more recent restoration work. This is probably the case for the drawing marked L4 (Studies of a horse’s front legs) in particular, which showed the least biodiversity and the heaviest contamination from human DNA. The authors further hypothesize that the recipe Leonardo used – “a preparatory layer made with powdered calcined chicken bones, lead white, indigo … mixed with animal gelatin” – may interfere with the preservation of the L4 microbiome, so only recent DNA remained.
But Piñar emphasizes that it is nevertheless very valuable to be able to track this type of data. “The sensitivity of the Nanopore sequencing method provides a great tool for monitoring artifacts. It makes it possible to assess the microbiomes and visualize their variations due to adverse situations,” she said. “This can be used as a bio-archive of the objects’ history, providing a kind of fingerprint for current and future comparisons.”
DOI: Microbial Ecology, 2020.10.1073 / pnas.1802831115
DOI: Frontiers in Microbiology, 2020.10.1007 / s00248-020-01504-x (About DOIs).