How bacteria are used to restore rare works of art in museums

After years of accumulating dust that have tarnished Michelangelo’s most famous marble statues in the Medici Chapel of Florence’s San Lorenzo Basilica, art restorers have begun a meticulous cleaning operation.

To do this, the scientists used a new procedure in which specialized strains of bacteria were released to feed on the dirt, restoring the shine to the maestro’s marble.

Art-restoring bacteria

For nearly a decade, experts from Italy’s National Research Council had been refurbishing the sarcophagi of the Medici’s final burial place. Most of the flaws on the artwork have been safely erased after years of painstaking and careful effort – all but a few stubborn spots that didn’t seem to respond to traditional restoration methods.

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Alessandro Medici, a former king of Florence who was killed in 1537 and buried in his family’s church without being properly gutted, is blamed for the mess. Compounds from Alessandro’s remains have seeped into the marble of some of Michelangelo’s statues in the chapel over the decades, leaving harsh stains that no cleaning agent could remove.

Finally, it was decided to use the bacteria to their full potential, transforming the marble ornamentation into massive petri dishes. But first, they had to select the appropriate strains.

Anna Rosa Sprocati, biologist, analyzed a database of over 1,000 strains. It was essential that she choose the right bacteria for the job. Some strains, for example, ate the grime as well as the marble of Michelangelo’s masterpieces. The repair effort could have easily turned into a disaster if a single mistake had been made.

Bacteria as art restorers
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Sprocati eventually landed on a shortlist of eight people, which she tested on a small area under the altar in the chapel. Serratia ficaria SH7, one of the bacteria, was exceptionally voracious, devouring Alessandro’s oils, glue, and all of the phosphates, leaving Michelangelo’s marble gleaming white. The bacterium is non-pathogenic to humans and does not produce spores.

The bacteria were first used to clean the marble from the tomb of Giuliano di Lorenzo, Duke of Nemours, decorated with the personification of night and day. Night’s hair and ears were previously covered in black soil, which had been wiped off by two distinct strains: Pseudomonas stutzeri CONC11, a bacterium isolated from tannery waste near Naples, and Rhodococcus sp.

ZCONT is a bacterium found in diesel-contaminated soil in Caserta. Night’s face has been treated with a stabilizer derived from the bacterium Xanthomonas campestris, which is commonly found in toothpaste and cosmetics.

Bacteria as art restorers
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Work was then abruptly halted due to COVID, with plans to resume in mid-October 2020. Sprocati resumed work, this time distributing SH7 bacteria gels on the grimy sarcophagus of Lorenzo di Piero, Duke of Urbino, Alessandro’s father killed.

A stain of history stained

All of these now immaculate treasures were commissioned by Pope Leo X, also known as Giovanni di Lorenzo de Medici, who planned a magnificent new sacristy as the final resting place for his illustrious family.

Naturally, they chose Michelangelo, the greatest artist of his time and a disciple of the Medici family since his teenage years. Michelangelo resumed construction of the magnificent mausoleum when Leo X died suddenly of illness in 1527, the year Rome was invaded by the mutinous forces of Charles V.

To take advantage of the situation, the Florentines planned a coup to depose the Medici and establish a republic. Alessandro, along with many other Medici, was expelled from the city, and Michelangelo supported this decision.

Alessandro was tough and uneducated, a lover of sensual pleasures who personally supported taxes and duties, and he was determined to establish his authority as total and unquestionable. He was often considered a tyrant by many. Michelangelo apparently could not tolerate Alessandro, according to historical accounts.

Bacteria as art restorers
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However, Michelangelo did not choose the victorious side, and the Medici returned to town soon after. Another Medici pope, Clement VII, pardoned Michelangelo in 1531, and he soon returned to work on the family chapel.

However, Alessandro had already ascended to the position of Duke of Florence by this time. Michelangelo couldn’t even sit in the same city as Alessandro, let alone in the same room, so he had to go back one more time.

A relative murdered Alessandro in 1537. His body was wrapped in a rug and thrown into a sarcophagus with little fanfare. When Michelangelo returned, he completed the work on the chapel this time. Alessandro would, however, taint his family’s reputation even decades later.

Fortunately, some voracious bacteria helped restorers complete the much-needed cleaning of the chapel. The chapel has been reopened to the public, allowing tourists to see some of Michelangelo’s most famous masterpieces in a new light.

Bacteria as art restorers
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This is not the first time that microorganisms have been used in the restoration of works of art. To remove black scabs from Milan Cathedral, sulfur-eating bacteria were deployed. Bacteria was also used to clean a mural on the dome of a cathedral in Pisa, as well as a cemetery near the leaning tower.

Could bacteria be used to clean the Taj Mahal?

In a recent interview with The Indian Express, Chiara Alisi, researcher in environmental microbiology, said, “We need to study marble first to understand if it is just dust and carbon particles causing the dark color or if there is formation of a biofilm. Biofilms form when communities of microorganisms adhere to a surface.

Taj Mahal
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Researchers from the Thapar Institute of Engineering and Technology in Patiala and Curtin University in Perth, Australia, presented a report in 2014 suggesting that calcifying bacteria could be used to remediate stones and heritage sites cultural site such as the Taj Mahal.

According to reports, the Archaeological Survey of India is planning to use bio-restoration techniques at the Taj Mahal.

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Christopher S. Washington