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The Church of Santos Juanes in Valencia, Spain.
Photo: Ivan Jurado

The frescoes in the Church of Santos Juanes in Valencia, Spain, have been damaged by fire (the Spanish Civil War), glue (botched restoration attempts in the ’60s), and salt blooms (a side effect of pigeon nests). But the 17th-century masterpieces aren’t lost yet. The Polytechnic University of Valencia’s Institute of Heritage Restoration and Centre for Advanced Food Microbiology have joined forces to rejuvenate the priceless works. Tool of choice: bacteria.

The idea is to use the harmless Pseudomonas stutzeri microorganism to clean the works in lieu of toxic chemicals or the jittery hands of restorers. “We grow the bacteria in a culture that has the substrate we want to eliminate,” says Pilar Bosch, a biologist who helped refine the method after studying with the team that cleaned Italy’s Campo Santo di Pisa (neighbor of the Leaning Tower). Effectively trained to eat salt and glue, the bacteria are brushed onto the frescoes and covered with a gel that, when heated with lights, creates humid conditions (perfect for nibbling) and aids cleanup. Just 90 minutes later, the surface is rinsed with water and dried, killing the bacteria. For the Pseudomonas, every masterpiece is the Last Supper.

Bosch and her colleagues have restored a third of Santos Juanes’ frescoes so far. When that’s done, they’ll team with startup Restaura BioTech to explore what other surfaces can be scrubbed by these hungry little technicians. They plan to offer their services to private clients, too—bacteria car wash, anyone?