Time and tourists are not the only bane of Paleolithic paintings; now, researchers have found that bacteria may ravage them too. Paintings in the famous Altamira cave of northern Spain host a thriving ecosystem of unknown--and potentially destructive--bacteria. The discovery marks the first time cave art pigments have been genetically tested for bacteria and suggests that new measures may be necessary to preserve the paintings.
Paleolithic paintings and engravings are humankind's oldest known forms of art. In caves visited by tourists, artificial lighting enhances the growth of algae and this often leads to colonization by bacteria. Decay may start even earlier. Some caves have a "natural" microbial population before they're opened to the public, says microbiologist Cesareo Saiz of the Spanish Scientific Research Council in Seville.
Previously, Saiz's team had found that many cave wall colonies contain a common soil bacteria. When Saiz and his colleagues analyzed red pigment from 16,000-year-old cave paintings near the city of Santander, they expected these cave-dwellers to dominate the samples.
Instead, genetic tests of the red pigment showed that the soil bacteria made up only 5% of the bacteria zoo. The rest consisted of acidobacteria--some strains of which eat iron oxide--and other bacterial types, the team reports in the 21 May issue of Federation of European Microbiological Societies Microbiology Letters. The discovery of acidobacteria is disturbing, the researchers point out, because iron oxide is the main coloring of red pigments. However, the team was unable to culture the bacteria found in the pigment, so the impact of the new strains on the painting remains unknown.
What's also unclear is whether reducing artificial lighting and cave visitors will protect the paintings, says microbiologist Orio Ciferri of the University of Pavia in Italy, who studies the microbial degradation of cultural artifacts. He says it will be important to monitor how the microbial populations vary over the years. That may start soon: A spokesperson for the regional government of Cantabria says that these findings have prompted authorities to consider closing the caves to tourists to allow Saiz to begin a year-long microbial study in September.