Restoring artwork using “debris-eating” bacteria, while respecting the original materials of the canvas and the environment—this is the technique developed by the ENEA-Rome Specialized Institute and applied in the Church of San Giacomo Parish in Soriso, Novara, on the 1730 painting The Martyrdom of Saint James Revealed by Tarquinio Grassi.

The artwork, placed on the back wall of the presbytery, was covered with a protective tissue in 2005 to shield it from damage during restoration work on the overhead vault. However, the canvas was never uncovered again. Removing the tissue, now stuck to the painting, risked causing severe damage. This is where bacteria came into play, thanks to an innovative intervention funded by Fondazione CRT and Fondazione Comunità Novarese.

But what exactly does the biocleaning process entail, and how was the most suitable bacterium for this specific intervention identified? On the occasion of the European Heritage Days on September 28–29, restorer Tiziana Carbonati and Chiara Alisi of ENEA Rome revealed the answers in an interview.

What is biocleaning, and how does it work?

Biocleaning relies on the ability of bacterial cells to produce enzymes capable of removing unwanted deposits or substrates of various origins. The process involves using live bacteria cultivated in large quantities (about a billion cells per milliliter of growth medium). These are centrifuged to remove the growth medium and immobilized within an inert gel.

In certain cases, the bacteria are applied in a “starved” state—kept in the gel without nutrients for at least 24 hours. This increases their “appetite” for the organic substrates that need removal, making the cleaning process more effective. The microbial cells, embedded in gel packs, can easily be applied to surfaces—even vertical ones or ceilings—and are just as easily removed without leaving residues.

This method is selective in targeting deposits, respects the original material, is safe for operators, and is easy to implement without stringent conditions for temperature or pH. Additionally, it poses no waste disposal challenges.

How does the restoration process work, and who is involved?

The biocleaning process involves applying the gel containing the bacteria onto the canvas’s protective layer, using an intermediate English tissue. A PVC film covers the application to slow the evaporation of water in the gel. The bacterial activity is monitored, with applications lasting from 4 to 12 hours depending on local conditions.

The team involved includes professionals from diverse fields:

• Edil Casa 2000 (Soriso) for the scaffolding setup,
• professional photographer Marco Bertoli,
• chemist Gianni Miani from Pro Arte Padova for pigment analysis,
• restorers Tiziana Carbonati, Chiara Metelli, and Cristina Fortina (Novara).

How was the “restorer bacterium” identified?

To target the adhesive used on the protective tissue, four bacterial strains from the laboratory’s collection were initially tested: Pseudomonas glycinis UT30, Microbacterium esteriaromaticus DAN5, Serratia ficaria SH7, and Sphingomonas dokdonensis TAR2. Each strain was tested in a gel medium to ensure its effectiveness in removing the adhesive without affecting the substrate.

Ultimately, Sphingomonas dokdonensis TAR2 was selected as the most suitable strain for the biocleaning process. This strain, originally isolated from an industrial plant in Sardinia, is an environmentally friendly strain classified as INAIL Risk Class 1, meaning it is safe for both operators and the environment.

Why was this innovative method chosen for this intervention?

The need to remove the protective tissue applied in 2005, which was originally intended for a restoration that never occurred, made traditional methods unsuitable. The innovative approach was developed in collaboration with Dr. Benedetta Brison (art historian) and Dr. Manuela Calligaris Ozino (restorer) from MIC_SABAP-NO.

Have you used this method before?

“This was my first experience using biocleaning and collaborating with the ENEA-Casaccia Institute in Rome, specifically with Dr. Chiara Alisi. It was a productive and positive cooperation for testing and applying this new method,” Carbonati shared.

Has this technique been applied in other cases in Italy or Piedmont?

Bacteria have been tested for biocleaning since the 1990s, with numerous case studies to date. Perhaps the most famous intervention was on Michelangelo’s marbles in the Medici Chapels, where Serratia ficaria SH7 was used to remove centuries-old residues in just two nights of work.

In Piedmont, the bacterial process has been tested for various issues, such as removing wax or lipid substances, with limited results. However, the TAR2 strain was successfully applied for the first time to remove animal glue with excellent results.

What does cultural heritage restoration mean to you?

“Cultural heritage restoration begins with planned studies to implement preventive maintenance. Restoration should be the last resort before losing the artwork entirely. These actions are essential for enhancing the value of cultural assets.”

What’s the most rewarding part of this work?

“Seeing how people are often amazed by the results achievable through simple or complex restoration operations. Observing how an intervention can save or slow the inevitable deterioration of a work, and knowing that your expertise has preserved it for decades, is incredibly fulfilling.”