In Carlo Bononi’s 17th-century painting of the coronation of the Virgin Mary, “Incoronazione della Vergine,” the lady herself takes center stage. She clasps her hands serenely as a golden crown is placed upon her head, surrounded by the Holy Trinity and a cohort of rosy-cheeked angels.
But in the 400 years since Bononi immortalized the Virgin Mary on the ceiling of a Christian basilica in Ferrara, Italy, a few unwelcome characters have joined this heavenly ensemble—and they’re making quite the meal out of this priceless piece of art.
As it turns out, natural pigments can turn a painting into a veritable smorgasbord for hungry microbes, imperiling the preservation of cultural artifacts. But, as scientists report today in the journal PLOS ONE, some bacterial species might be able to guard works of art from their more nefarious relatives. If the new findings pan out, this unusual brand of probiotic may someday bolster the toolkit of art conservation.
Study author Elisabetta Caselli, a microbiologist at the University of Ferrara in Italy, has spent the past several years hunting the infectious microbes that tend to lurk in hospitals. Faced with drugs and decontaminants, many microscopic invaders have a nasty habit of evolving resistance, leading Caselli and her colleagues to take a different tack: unleashing friendly microbial species to drive out their more harmful colleagues. On nearly every surface around us, microbes are duking it out for space and nutrients, and the vast majority of them mean no harm to humans. Rather than relying on repeated rounds of sterilization, so-called probiotic sanitation takes advantage of natural microbial diversity to effectively fight fire with fire—and Caselli’s team has already reported a few early successes in patient wards.
The same logic, the researchers reasoned, might be applied to other surfaces rife with microbes. Oil on canvas paintings may not be the first of these locales that come to mind, but textiles, binding agents, oils, wood, paper, and pigments can all serve as hearty fodder for bacteria and fungi alike, especially in warm, humid environments.
Bononi’s masterpiece, rendered around the year 1616, fit the bill. For nearly four centuries, it adorned the ceiling of the Christian Basilica of Santa Maria in Vado, Italy, until a 2012 earthquake prompted its removal. In the years following, the painting was left exposed against a church wall, where it continued to accumulate wear and tear. But when restoration efforts began, Caselli and her colleagues eagerly leapt at the chance to participate. Because of the artwork’s significance to local culture, Caselli says, “all of us were also highly emotionally involved.”
To minimize damage to the painting, the team sampled only a few locations on the front and back of the canvas, some of which had sustained damage from the earthquake. Focusing their efforts on microbes that they could culture and grow in the lab, the researchers identified several species of bacteria, yeast, and fungi. Caselli was surprised to find that certain species of fungi seemed to thrive better on specific pigments: Dark brown and red colored areas—like the angel’s earth-colored clothing or the crimson cloak of the Father—fed molds like Aspergillus and Penicillium (the genus that includes the original source of the antibiotic penicillin), while lighter areas colored yellow or pink facilitated the growth of Cladosporium. The team still needs to figure out exactly what’s contributing to this species segregation, Caselli says, but it could have something to do with the nutrients contained in specific pigments, or environmental conditions like temperature and light exposure.
Caselli and her colleagues then tested if probiotics could halt the growth of these pint-sized vandals. As in their previous work in hospital environments, dormant spores from bacteria in the Bacillus genus were able to overtake the growth of the microbes isolated from the painting’s surface in petri dishes. Though the researchers have yet to repeat these experiments on actual paintings, Caselli is hopeful that this technique will someday prove itself to be a useful alternative to chemical decontamination.
Others, however, are slightly more hesitant to give painting probiotics the green light. The formation of spores is a way for bacteria that find themselves in less-than-ideal conditions to go into hibernation until the forecast improves; as a result, spores are low-maintenance tenants that can still exude chemicals to keep other species at bay. But introducing bacteria—in any condition—onto the surface of the painting may pose a risk, points out Ji-Dong Gu, an environmental microbiologist at the University of Hong Kong who did not participate in the new research. Once spores reawaken, they need to eat, too.
In fact, other Bacillus species were among those found on Bononi’s painting. However, Caselli explains that the potentially probiotic Bacillus have different nutritional needs than their art-munching relatives, and may be able to guard artwork without compromising its integrity. She hopes to confirm this theory with future work.
Still, there may be other important microbes defacing paintings such as Bononi’s that weren’t identified in this study, Gu says. The researchers restricted their search to microbes that grew in laboratory conditions, rather than probing for DNA, which would capture the presence of species both dead and live. As a result, many microbes were likely left out of the final picture—and some may not be as vulnerable to the researchers’ super-powered spores.
“This work gives us a nice case study,” says art conservator Kristin deGhetaldi. “It alludes to a possible path forward, but any new treatment needs to be tested extensively first to make sure there are no adverse effects.”
To dissuade the growth of microbes, conservators prioritize storing works of art in controlled environments with low humidity and cool temperatures. But when conditions aren’t ideal—or when damage has already occurred—preservation of a painting necessitates treatment alongside prevention. If the probiotics pan out, they could have wide-reaching benefits for not only artwork, but also conservators themselves, says Fernando Poyatos, who studies the role of microbes in art conservation at the University of Sevilla in Spain. The chemicals used to decontaminate paintings, like ammonium salts and phenols, can be hazardous to health, Poyatos explains. Most Bacillus species, on the other hand, are happy to peacefully coexist alongside their human cultivators.
For now, scientists are far from smearing swaths of bacteria onto the world’s most prized cultural relics. But depending on how this microbial war shakes out, we may yet find that some of our most powerful art conservators might also be our smallest.
And in the meantime, these creative tactics are opening new and unexpected doors for communication between diverse fields of science, says conservation scientist Aaron Shugar of Buffalo State College, who did not participate in the research. “This shows how exciting conservation science really is,” he adds. “We’re happy when other scientists want to explore something with us... to explore this craft with novel ideas.”