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Thursday, April 18, 2024

Meet the Microbes Living on Da Vinci’s Iconic Sketches

As many prominent historians have noted, Leonardo da Vinci invented the bejesus out of things. He dreamt up the helicopter and the diving suit and a 33-barreled cannon because sure, why not? But there’s no way he saw this one coming: Half a millennium after da Vinci’s death, scientists have sequenced the DNA that has over the years become slathered across seven of his drawings, fully mapping the microbiomes of bacteria and fungi that tell fascinating tales of the priceless works’ life histories.

The goal of the study was to not only characterize the unique microbiomes found on these masterpieces, but to begin to understand how they might change when art travels between different institutions. Get a handle on that, the thinking goes, and conservators can better monitor artworks for microbial nasties, like fungi that eat away at paper.

Researchers in Italy and Austria took five da Vinci drawings from the Royal Library of Turin and two from the Corsinian Library in Rome, including his famous self-portrait the Man in Red Chalk, and carefully dabbed each of the surfaces with sterile membranes made of cellulose nitrate. They also attached membranes to the end of gentle suction tubes, and hoovered the microbes up that way, without touching the drawings. (Snipping off a sample of the paper would be—shall we say—frowned upon.)

“In any other environmental study, you can go there, you can take kilos of soil or liters of water. But we cannot take samples,” says Guadalupe Piñar, a microbiologist at the University of Natural Resources and Life Sciences in Vienna and lead author on a new paper describing the work in the journal Frontiers in Microbiology. “So we have to live with these tiny samples that we get to obtain all the information.”

What made this possible is a powerful new “nanopore” genetic sequencing device from Oxford Nanopore Technologies. It uses fewer reagents and chemicals to process the samples than do previous generations of sequencing technology, Piñar says, and the device is small enough to fit in your pocket. “So, theoretically, you can take the device everywhere and do the sequencing on-site—imagine also being able to sequence in museums or archives,” says Piñar. The sequencer is sensitive enough to take what little DNA the researchers could dab off the drawings and identify a dizzying array of microbes. The team could then tease apart the microbes’ life cycles based on their origin.

“Of course, we found many bacteria related with the skin microbiome,” says Piñar. “So when you are touching it, you are leaving your own microbiome there.” You might be thinking: So does that mean we now know what was crawling on da Vinci’s hands when he drew these masterpieces? Sadly, no, as the drawings have been handled by many, many other people in the five centuries since the master sketched them out. And to be clear, this genetic sequencing didn’t tell the researchers whether all these bacteria were dead or alive—just that they were present in some form.

Among human skin microbes, the researchers found high levels of the bacteria genus Moraxella, particularly Moraxella osloensis, which is responsible for the stink of dirty laundry. In addition, they detected the infamous bacteria Salmonella and E. coli., both of which bring turmoil to the human gut. They also found bacteria species specific to the guts of common flies and fruit flies, meaning that bugs had been brazenly defecating on priceless works of art—at least until someone put them into impeccably clean drawers for storage, or behind glass where they’re displayed, sealed up and kept at the perfect temperature and humidity. “As the drawings are nowadays conserved, there's no way that insects can go in and, you know, make their things there,” says Piñar. “It is not possible anymore. So you have to think this could have come from the times when the drawings were not stored like they are now.”

Piñar and her colleagues also found Aspergillus, a mold that’s dangerous for some people to inhale, and detected species of the genus Penicillium, the fungus that gave us penicillin. Most worryingly for both the artworks and the conservators who handle them, the analysis turned up the fungus Alternaria, known as a “paper-spoiler” for its habit of … spoiling paper. It’s also an allergen that can be dangerous to inhale.

The team also found the fungi responsible for the “foxing” of paper, or the yellow-brown spots that form over the years. In addition to the DNA analysis, the researchers scoured the surface of the drawings with a microscope and spotted incrustations of calcium oxalate crystals produced by these fungi. “So you can infer a lot with this microscopic analysis and complement very well the molecular analysis that we do here,” says Piñar.

The artworks are now kept in conditions that prohibit the growth of these fungi, but that doesn’t mean they can’t come roaring back if the works aren’t stored properly. “Therefore,” says Piñar, “the most important message is to identify the possible microbial risk in order to adapt the environmental conditions of storage in such a way that they cannot allow the germination or the proliferation of microorganisms, in this case the control of environmental parameters such as temperature, humidity, and clean air.”

Zooming out to take a look at the drawings as a whole, the researchers found intriguing similarities among the microbes living on them. “We could see really that the microbiomes were grouping according to their geographical location,” says Piñar. “So we could see more similarities among the drawings located in Turin, and between the two drawings located in Rome—so actually there should be a geographical influence, or in the storage conditions of these places.”

Next, Piñar and her colleagues can begin to build a sort of database of the microbiomes sampled from masterpieces, comparing the bacterial and fungal communities between works from within the same collection and from others. They might also explore how different materials, like canvas and paper, promote or discourage the proliferation of different microbial species. And, critically for the preservation of these treasures, conservators might test the microbiome of a work for signals of an impending attack by, say, a paper-spoiling fungus that’s begun to take hold but hasn’t yet spread widely.

“It's like saying, OK, there's an army in your country that has a weapon, and it can use this weapon to spoil your—in this case—artifact,” says microbiologist Massimo Reverberi of the Sapienza University of Rome, who wasn’t involved in the research. If a conservator can’t yet see the effects of the fungus visually, perhaps the microbe’s DNA could betray its presence. “And when there is a trigger—that could be global warming—it could start to do some of its spoiling activity.”

Luckily, conservators just got a 33-barreled genetic cannon to fight off the microbial menace.

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