Top secret experiment for Medici Chapels: team unleashed dirt-eating bacteria on marbles

Dirt-eating bacteria have been secretly cleaning up Michelangelo ’s marvelous sculptures in the Medici Chapels: in fact, last fall, taking advantage of reduced hours due to the pandemic, a team of scientists and restorers performed an innovative experiment, releasing particular dirt-eating bacteria onto the marbles. This was revealed in an article in the New York Times.

The all-female team is made up of Donata Magrini, Anna Rosa Sprocati, Daniela Manna, Paola D’Agostino, Monica Bietti and Marina Vincenti, and the bacterium in question is Serratia ficaria SH7, employed as a biological weapon to devour centuries of stains deposited on the chapel’s marble. Stubborn stains had remained despite restorations that had removed most of the dirt, so further intervention was necessary, a “top secret” experiment, as one of the restorers Daniela Manna called it. “SH7 ate Alessandro,” said Monica Bietti, former director of the Museo delle Cappelle Medicee, referring to Alessandro de’ Medici, to whom, according to one hypothesis, the cause of the stains is traced, since he was buried in the tomb inadequately eviscerated, causing deep stains and deformations on the marble.

The experiment started as early as November 2019, when the Medici Chapel Museum brought in the National Research Council, which performed infrared spectroscopy, revealing calcite, silicate and other organic remains on the statues and tombs. From this discovery, Italian National Agency for New Technologies biologist Anna Rosa Sprocati conducted a selection, out of nearly a thousand strains, of the most suitable bacteria: some of nearly “ate” phosphates and proteins, but also marble. On a small portion of the marble surface behind the altar, the eight most “devouring” strains were finally tested.

The first tomb to be tested by the bacteria was that of Julian, Duke of Nemours, specifically the highly polished statue of Night, and the result was surprising. Then it was the turn of the tomb of Lorenzo, Duke of Urbino. Bacteria did an excellent job of cleaning it, and now the New Sacristy shines thanks to an organic and non-aggressive intervention.

Ph. Credit Andrea Jemolo

Top secret experiment for Medici Chapels: team unleashed dirt-eating bacteria on marbles

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