THE IMPACT OF MICROORGANISMS - ESPECIALLY NITRIC ACID PRODUCING BACTERIA - ON THE DETERIORATION OF NATURAL STONES

Summary Chemolitho– and chemoorganotrophic bacteria as well as fungi, algae, and cyanobacteria are involved in the deterioration of natural stones, bricks and concrete. Up to now 16 important historical buildings have been tested for the presence of microorganisms. They were detected in high numbers at every building. Nitrifying bacteria were as abundant as the other groups. They were found to depths of 30 cm in sandstones (endolithic bacteria). Their substrate ammonia is deposited by dry or wet mechanisms from the anthropogenically polluted atmosphere on the surface of buildings. Ammonia originates from livestock breeding, intensive farming, and industry. Nitrifying bacteria consist of 2 groups. The most frequent ammonia oxidizing bacterium in sandstone is Nitrosovibrio , an organism, which had been demonstrated previously only in acid tea soils of Hawaii and in Wales. This genus may turn out to be a marker for biogenic deterioration of natural stones. The nitrite oxidizing bacteria belong to the genus Nitrobacter . The importance of these bacteria was proved by simulation experiments, where the conditions for the bacteria had been optimized. At 28°C, a relative humidity above 95%, and an unlimited supply of ammonium chloride deterioration of sandstone and concrete test blocks was noted within one year. The blocks lost 3,5% of substance (average) during incubation. An active population grew on and in the test blocks.