As a once-in-a-century virus either shut down or restricted the open hours of the world’s great museums, art restorers in Italy worked to rid a priceless Michelangelo of centuries of accumulated dirt and grime. They let loose the bacteria.
Art restorers have usually employed chemical agents and, more recently laser techniques, to remove dirt, oil, glue, or pollutants from monuments, stoneworks, and paintings. But since the 1980s, when researchers first used the bacteria Desulfovibrio vulgaris to clean a marble monument at the Cave Hill Cemetery in Louisville, US, the role of micro-organisms has been recognised in protecting the artistic heritage of humanity.
D vulgaris went on to meet several artworks, including, in 2013, the Allegoria Della Morte — the Allegory of Death — at the English Cemetery in Florence. Art restorers from the Opificio Delle Pietre Dure museum allowed the bacteria to eat away the thick black crust that had veiled the beauty of the blindfolded skeleton statue taking a scythe to a bunch of flowers, carved by Giuseppe Lazzerini in 1870.
Calling in the bugs
Environmental microbiology researcher Chiara Alisi, who was part of the team that restored one of Michelangelo’s masterpieces in the New Sacristy at the Medici Chapels in Florence during the 2020 lockdowns, told The Indian Express over Zoom from Rome:
“At our lab in ENEA (Italy’s national agency for new technologies and sustainable development), we have over 1,500 bacteria that like to eat different enzymes. My first bio restoration in 2014 was on a 16th-century wall painting. We screened the bacteria we had with us and selected three that could digest protein. The living bacterial cells were suspended in a gel and applied to the vertical walls and left for 24 and 48 hours. The bacteria did not disappoint us, they did their job well. When the gel was removed, we saw that the inorganic dark brown layer and also the other deposits were removed.”
The New York Times, which first reported the initially secret restoration in Florence, said the team washed the hair of one of the marble statues with Pseudomonas stutzeri CONC11 bacterium isolated from the waste of a tannery near Naples, and cleaned the residue of casting moulds, glue, and oil using Rhodococcus sp. ZCONT, another strain that came from soil contaminated with diesel.
Bio-cleaning on the front surface of the Triumph of Death fresco in Pisa; (right) after the treatment. G. Ranalli et al. (Source: Journal of Applied Microbiology (2018)
Faith in Pseudomonas
Over the past decade, Dr Pilar Bosch Roig, a specialist in bio-cleaning and bio-deterioration of artworks in Spain, has trusted P. stutzeri to clean a range of monuments, as well as the stones of historic bridges and granite slabs of chapels in Spain.
She told The Indian Express in an email that over a decade ago, this strain of bacteria was used for the bio-restoration of frescoes in the 17th century Church of Santos Juanes in Valencia, Spain, and murals of the Camposanto Monumentale di Pisa in Italy.
A team led by environment microbiologist Giancarlo Ranalli from the University of Molise in Campobasso, Italy, recently used P. stutzeri to clean the 14th century Triumph of Death fresco at the Campo Santo. The cemetery was bombed during World War II.
Dr Ranalli’s team arrived in 2018, and applied the bacterial suspension on the fresco, and after three hours “the bacterial activity was so intense that the treated areas were largely bio-cleaned and no residues of proteinaceous materials were present,” according to a paper published in the Journal of Applied Microbiology.
“The treatment was soft and delicate and did not show any structural damage,” the authors reported.
“There is a general notion that bacteria are harmful,” Alisi said. “But not all are pathogens. In fact, our lab is not allowed to use pathogens. Also, these bacteria are not modified or genetically engineered. They are just common ones from natural environments that love to eat various proteins and we are just using them to save our beloved artworks.”
Could they clean Taj?
On whether these bacteria could be used to fix the discolouration of the Taj Mahal, Alisi told The Indian Express: “We first need to study the marble to understand if it is just dust and particulate carbon causing the dark colour or if there is a biofilm formation.”
Biofilms are formed when communities of microorganisms adhere to a surface.
Dr Archana Tiwari, associate professor at Amity Institute of Biotechnology in Noida, expressed confidence that bio-restoration can save many of India’s monuments. “We have tested these bacteria and now have a repository. The technology needs to move from lab to field and we can see our monuments like Taj Mahal get a new life,” she said.
In 2014, a paper published by researchers from Thapar Institute of Engineering and Technology, Patiala, and Curtin University in Perth, Australia, noted that calcifying bacteria could be used for remediation of stones and cultural heritage monuments, including the Taj Mahal.
The Archaeological Survey of India is learnt to be exploring the option of employing bio-restoration at the Taj.
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Bio-cleaning on the front surface of the Triumph of Death fresco in Pisa; (right) after the treatment. G. Ranalli et al. (Source: Journal of Applied Microbiology (2018) 
Bio-cleaning on the front surface of the Triumph of Death fresco in Pisa; (right) after the treatment. G. Ranalli et al. (Source: Journal of Applied Microbiology (2018)
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