Apr 4, 2013

Stone-eating bacteria

Stone-eating bacteria belong to several families in the genus Thiobacillus. They can cause damage to monuments, tombs, buildings, and sculptures by converting marble into plaster. The principal danger seems to come from Thiobacillus thioparus. This microbe's metabolic system converts sulfur dioxide gas (found in the air) into sulfuric acid and uses it to transform calcium carbonate (marble) into calcium sulfate (plaster). The bacilli draw their nutrition from carbon dioxide formed in the transformation. Nitrobacter and Nitrosomonas are other "stone-eating bacteria" that use ammonia from the air to generate nitric and nitrous acid. Still other kinds of bacteria and fungi can produce organic acids (formic, acetic, and oxalic acids) which attack the stone as well. The presence of these microbes was first observed by French scientist Henri Pochon at Angkor Wat, Cambodia, during the 1950s. The increase of these bacteria and other biological-damaging organisms that threaten tombs and buildings of antiquity are due to the sharp climb in the level of free sulfur dioxide gas in the atmosphere from automotive and industrial emissions. (The Handy Science Answer Book, compiled by the Science and Technology department of the Carnegie Library of Pittsburgh)