Biodeterioration vs biodegradation: the role of microorganisms in the removal of pollutants deposited on historic buidlings

This paper describes some biodegradation processes originating from the activity of microorganisms in the black crusts of historic buildings. The crusts are mainly composed of gypsum, carbonaceous particles, and polycyclic aromatic hydrocarbons. The slowly dissolving gypsum from black crusts represents a continuous source of sulphur for microbial growth. The sulphate-bonding capacity of the sheath of cyanobacteria causes a particularly high demand for sulphate, thus making sulphur nutrition a relevant aspect in their physiology. On the other hand, bacteria capable of using polycyclic aromatic hydrocarbons as a sole carbon and energy source were isolated from monuments. These examples illustrate that on the surfaces of building stones, located in polluted environments, there is a continuous deposition and, at the same time, a biodegradation of pollutants leading to their removal. Resumen Se describen algunos procesos de biodegradación estudiados en constras negras de edificios históricos. Estas costras, formadas mayoritariamente por yeso, particulas carbonáceas e hidrocarburos policiclicos aromáticos, son, por una parte, una importante fuente de azufre, necesaria para la síntesis de los polisácaridos de las vainas de cianobacterias. Por otra, algunas bacterias utilizan los hidrocarburos policíclicos aromáticos como fuente de carbono y energía. Estos ejemplos indican que, junto a la deposición de contaminantes sobre la superficie de los monumentos, existe una variada actividad microbiana que conduce a su biodegradación y eliminación.