Rome may be the eternal city, but its ancient artifacts are under unrelenting assault by 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 one, has the grime of 18 centuries caked onto its surface.
Now, conservator Alessandro Lugari and his colleagues are trying to salvage the city's treasures using a new technology -- one that employs one of the oldest forms of life: bacteria.
"This marble was almost disintegrating; it was turning to powder," he says. "So we needed to intervene with consolidation."
Standing beneath the arch, Lugari points to a marble block weighing several metric tons. "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 covered with enzymes, drawing the bacteria -- which naturally reside within the marble -- to the surface. The resulting calcification strengthened the stone, with the enzymes applied multiple times a day over the course of two weeks.
"(The bacteria) doesn't pass through the marble but rather through the cracks, and it solidifies," Lugari explains. "It becomes covered with calcium carbonate, which is the same substance as marble and therefore binds, on a microscopic level, the various parts of the marble, creating more marble.
"We tried this, it worked, so the next step will be to try it on the entire monument," he adds.
RESTORING AT THE MOLECULAR LEVEL
Silvia Borghini, conservator at the National Roman Museum, said that 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 pathogens," she says. "More than 95 per cent of bacteria are not harmful to humans... we live in the midst of bacteria and live thanks to bacteria."
Increasingly, restoration work is being carried out on a molecular level. But in Italy, the challenge is huge because the country has archaeological sites on a monumental scale.
Beginning 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 with the Italian National Agency for New Technologies. "But in this case using chemical substances would have been too aggressive, so (the restorers) asked for our help."
Alisi and her team search for potentially useful strains of bacteria in industrial waste sites, abandoned mines and sites from the distant past, like ancient tombs.
"They've already been selected by nature to develop potential abilities, which we can test, and study and apply," she explains.
It's a complicated process -- isolating individual strains that thrive on the right kinds of filth, sequencing their DNA and then putting them to work.
Borghini demonstrates the results in the garden of the National Roman Museum. With a toothbrush she removes gel suffused with bacteria from a block of marble, once part of a 4th-century Roman bridge. Out of the test strips, each of which tried different bacteria strains, the cleanest was covered for 24 hours with one known as SH7.
"(Bacteria is) easy to apply, and afterwards the artifacts stay clean," she says. "It doesn't harm the environment, it's not toxic for us or the flora in the garden. It's perfect."
