Endolithic colonization of stone in six Jewish cemeteries in urban environment.

Biological growth on gravestones of six Jewish cemeteries located in two towns (Padua and Rovigo) in northern-eastern Italy was studied. The presence of endolithic microorganisms (cyanobacteria and fungi) is the most diffuse alteration of the stone. Their colonization gives rise to discoloration of the stone to grey-black, more or less enhanced, and creates evident damage due to the formation of micro-holes resulting from the solubilization of the substrata. Black colour is due to the pigments of meristematic fungi and cyanobacteria, which have a lighter colour when penetrating deeply in the stone. In vertical or inclined surfaces cyanobacteria communities prevail and penetrate about 100 µm, while meristematic fungi are present in less extent. On horizontal surfaces (e.g. sarcophagi and plinths) primary colonizers, and frequently the only ones, are fungi, which derive organic matter from the decomposition of leaves of plants and soil dust. Generally fungi penetrate deeper, up to 500 µm. Endolithic colonization is related to areas with higher water supply due to the inclination or to preferential flows induced by the shape of gravestone or the presence of sculptural elements. Marble is the kind of stone which is deeply penetrated by microorganisms (up to more then 3 mm), as it is very deteriorated showing large intergranular spaces.