Ciferri, O.
1999
Appl Environ Microbiol., 65 (3): 879-885
| In 1940 four young men discovered the Lascaux Cave in the Dordogne region of France. The cave contained an impressive display of prehistoric art: the main cavern and several galleries connected to it were decorated with engraved, drawn, and painted figures of animals. The approximately 600 paintings, done with mineral pigments mixed with animal fat in various shades of yellow, red, brown, and black, were dated to the late Aurignacian period (15,000 to 13,000 B.C.). With few exceptions, the paintings, some as long as 5 m, represented different animals (some imaginary), and their quality was such that the cave was designated by some the Sistine Chapel of the Paleolithic. In 1948 Lascaux Cave was opened to visitors, but in 1963 it was closed indefinitely to the public. Closing was imposed after the discovery of a green patina (from which comes the term maladie verte, or green disease) covering the painted portions (34). Quite unexpectedly, although other algae together with cyanobacteria, bacteria, and fungi were isolated in different parts of the cave, the green patina was composed exclusively of the unicellular alga Bracteacoccus minor (order Chlorococcales). The influx of workers and visitors brought into the cave considerable amounts of soil and of the organic compounds present in people's breath and sweat and increased the concentration of carbon dioxide to almost pathological levels. The lighting system, installed in the cave and operating almost continuously, created the conditions for a massive growth of photosynthetic organisms. Extensive analysis of the composition of, and the variations in, the microbial population of the painted areas as well as of the unpainted rocks and the surrounding environment led to the conclusion that the population of Bracteacoccus minor, responsible for the maladie verte, also increased when the cave was closed to the public and kept in continuous darkness for long periods. Indeed, after 3 months of total darkness and closure to the public, algal proliferation on painted areas was found to have increased by 1 order of magnitude (35). Thus, it was concluded that the alga could grow even under heterotrophic conditions by utilizing the organic molecules brought in the cave by visitors or resulting from the degradation of biological residues. It was postulated that, before discovery and opening of the cave, the community of heterotrophic microorganisms, bacteria and fungi, present in the cave had mineralized all organic molecules present, so that heterotrophic growth of the alga was prevented, as was autotrophic growth as a result of the absence of light.
The Lascaux Cave is perhaps the most emblematic example of the damage that microorganisms may cause to art work and should settle once and forever the arguments about the possible role of microorganisms in the degradation of our cultural heritage. The conditions that led to the microbial bloom on the Lascaux Cave paintings probably represent an extreme case, but it may be argued convincingly that even less harsh environmental stresses than those that occurred in the less than 20 years since the opening of the Lascaux Cave may cause irreversible aesthetic and structural damage to almost any type of art work.
This minireview focuses on the colonization of art works by microorganisms and its effects. Its scope will be limited to paintings, both on canvas and panel, as well as on walls. Thus, other art works, such as those in stone, wood, paper, and masonry, as well as those in more esoteric materials, such as leather, parchment, glass, and metal, will not be considered. For a more comprehensive treatment of the role of microorganisms in the degradation of our cultural heritage, the reader should refer to the reviews already published (2, 6, 12, 13, 20, 29, 30, 36, 46, 55, 56). The treatment of the subject will not be exhaustive but will focus on aspects that, in the writer's opinion, appear to be most interesting. At the end, a few ideas on how, again in the writer's opinion, the research in this field might proceed will be expressed. |
