Ever since the Da Vinci Code came out a couple of years ago, people have gotten really interested in ancient art. I initially thought “ancient art” would be something more…I don’t know…ancient. Like from the Greco-Roman Era. Indeed, these scientists (Italian, of course) were referring to Medieval and Renaissance art. The point of the study was to determine a) if the “rosy discoloration” of the fresco “The Crypt of the Original Sin” in Italy was from bacteria and if it was, b) what species were the culprit.
The idea that bacteria could cause the deterioration of paintings was hardly new; in fact, lithotrophs (bacteria that can use inorganic compounds, such as iron and sulfur) have been used to aid the restoration of paintings. Given the location of the painting within the cathedral, the scientists hypothesized that the contamination was microbiological rather than chemical. They took a sterile scalpel and scraped a tiny bit of the discolored paint off of the fresco- approximately 1 mm square. They amplified any bacterial DNA using PCR, focusing in on the 16S rRNA genes. Since each species of bacteria has a distinct 16S rRNA gene, identification would be fairly straightforward. Portions of the gene were sequenced, and the bacteria were identified using a BLAST search. The predominant species of bacteria was Rubricobacter radiotolerans. Quantitative PCR found species from Archaea to be a minority of the species found in the discolored areas. Raman spectroscopy (as opposed to the better known Ramen Noodle Soup, staple of poor college kids) was used to confirm the identity of the bacterial species. A sample of the discolored paint was compared to a pure colony of Rubricobacter radiotolerans, which provided an almost exact match.
The authors write:
Rubrobacter radiotolerans shows the characteristic reddish pigmentation due to the presence of two main C-50 carotenoids, namely bacterioruberin and monoanhydrobacterioruberin…
The specific color spectrum of these bacterial pigments matched the color spectrum of the discoloration of the fresco on the “The Crypt of the Original Sin.” The authors of the study believe that an abnormally hot and dry “spring-summer period,” along with restoration efforts that increased daylight UV rays, may have “promoted the outgrowth of xerotolerant heterotrophic bacteria, primarily Rubrobacter spp., at the expenses of the preexisting microbial community.”
Source: Imperi F, et al. “The bacterial aetiology of rosy discoloration of ancient wall paintings.” Environmental Microbiology, 2007, 9(11), 2894-2902.