Published on Science of the Total Environment, May 2025 | DOI: 10.1016/j.scitotenv.2025.179494
Michelangelo’s “secret room” beneath the Medici Chapel in Florence has always fascinated visitors and scholars with its stunning charcoal sketches. But recently, something unexpected has caught researchers’ attention: a curious pink discoloration creeping across the lower parts of its walls.
Was this a pigment? A result of past restorations? Or perhaps… alive?
Thanks to a groundbreaking interdisciplinary study, an international team led by CNR-ISPC, with the collaboration of CNR-INO, CNR-IPSP, the Opificio delle Pietre Dure, and the Bargello Museums, has cracked the code. The pink stains, it turns out, are not the work of an artist or restorer—but of tiny, salt-loving microorganisms from the domain of Archaea!
Using a combination of high-tech tools—Raman spectroscopy, environmental sensors, scanning electron microscopy, and advanced DNA sequencing—the team discovered that the discoloration is caused by Halalkalicoccus sp., a type of extremophilic Archaea that thrives in salty environments. These microbes produce carotenoid pigments (similar to those in carrots), giving the walls their distinctive hue.
Although the room is carefully preserved and protected, tiny fluctuations in temperature and humidity—especially in warmer months—create just enough moisture to activate salt movements within the plaster. These salts attract halophilic microorganisms, which feed off the environment and slowly spread their pinkish signature.
This is the first time that Halalkalicoccus has been both isolated and identified through culture and metagenomic techniques in a heritage context. It’s also one of the few studies to combine lab and in-situ (on-the-spot) spectroscopy to trace microbial pigments back to their microbial authors. The findings enrich our understanding of microbial biodeterioration and open up new conservation strategies for fragile heritage environments.
The “secret room” continues to reveal its mysteries—this time through science. While the drawings remain untouched, the study highlights how the microclimate, previous restorations, and even microscopic life can impact artworks centuries after their creation.
Next time you step into a historical site and see a strange color on the wall, remember: it might just be a microbial masterpiece.
Read the full paper at this link