Historic stone objects, being mineral substrata, are colonized
mainly by an autotrophic microbiota, which causes
serious devastation particularly in the lower parts of buildings
and in the parts of stone objects touching the ground.
Particularly active here are sulphur bacteria, which penetrate
into the stone with the ground water and because of
their microaerophily are able to live and reproduce inside
the pores, even as deep as 5 cm below the surface of the
stone. Their numbers can reach 1:4 × 106 cells g−1 stone
(Pochon and Jaton, 1967). The autotrophic process of oxidation
of reduced sulphur compounds results in the formation
of sulphuric acid, can reach a concentration as great
as 5%. Whenever it is produced, the acid reacts with the
calcium carbonate (in limestone or sandstone with calcareous
binder) weakening the structure and forming hydrated