The latest technology in art restoration? Bacteria

(CNN) – Rome may be the eternal city, but its ancient artifacts are subjected to the ravages of time, pollution, acid rain, and the sweat and breath of millions of tourists. The Arch of Septimius Severus in the Roman Forum, for example, has 18-century dirt on its surface.

Now, curator Alessandro Lugari and his colleagues are trying to save the city’s treasures with a new technology that uses one of the oldest forms of life: bacteria.

“This marble was almost disintegrating; it was turning to dust,” he says. “So we had to intervene.”

Standing under the arch, Lugari points to a multi-ton block of marble. “Inside there are billions of bacteria,” he adds.

The block in question served as a test for the rest of the monument. Its exterior was coated with enzymes, attracting bacteria – which naturally live in marble – to the surface. The resulting calcification strengthened the stone, and the enzymes were applied several times a day for two weeks.

“(The bacteria) do not go through the marble, but through the cracks, and it solidifies,” explains Lugari. “It is covered with calcium carbonate, which is the same substance as marble and, therefore, unites, at a microscopic level, the different parts of the marble, creating more marble.”

“We have tested it and it has worked, so the next step will be to test it on the entire monument,” he adds.

Restoration at the molecular level

Silvia Borghini, curator at the National Roman Museum, says bacteria have an unfair reputation because they are associated with infection, but their functions are much more complex. “Only a very small number of bacteria are pathogenic,” he says. “More than 95% of bacteria are not harmful to humans … we live in the midst of bacteria and we live thanks to them.”

Increasingly, restoration work is being carried out at the molecular level. But in Italy, the challenge is enormous because the country has archaeological sites on a monumental scale.

Starting in November 2019, bacterial microbes were used in Florence to clean the Medici Chapel, a mausoleum designed by Michelangelo in the 16th century.

“They found that they had to remove both organic and inorganic materials,” says Chiara Alisi, a microbiologist at the Italian National Agency for New Technologies. “But in this case using chemicals would have been too aggressive, so (the restorers) asked us for help.”

At the National Roman Museum in Rome, multiple test strips with different strains of bacteria were tested on marble blocks. (Photo: CNN)

Alisi and her team search for potentially useful strains of bacteria in industrial landfills, abandoned mines and places from the distant past, such as ancient tombs.

“They have already been selected by nature to develop potential capabilities, which we can test, study and apply,” he explains.

It’s a complicated process: isolating the individual strains that thrive in the right kinds of dirt, sequencing their DNA, and putting them to work.

Borghini demonstrates the results in the garden of the National Roman Museum. Using a toothbrush, he removes the bacteria-impregnated gel from a block of marble that was part of a 4th-century Roman bridge. Of the test strips, each of which tested different strains of bacteria, the cleanest was coated for 24 hours with one known as SH7.

“(The bacteria are) easy to apply, and then the appliances stay clean,” he says. “It does not harm the environment, it is not toxic for us or for the flora of the garden. It is perfect.”