Dematiaceous fungi as a major agent for biopitting on Mediterranean marbles and limestones

Experimental evidence is presented for the first time, that dematiaceous fungi with yeast-like growth patterns can actively penetrate rocks and cause loss of rock material, thus creating biopitting. Fungal strains inoculated onto Carrara marble cubes and submitted to alternating periods of humid and dry conditions produced biopits with a size of up to 500 mu m within a period of 10 months. The type and geometry of biopits, however, were independent of the fungal genus causing the pit. Analysis of 22 field samples taken from monuments in the Sanctuary of Delos (Cyclades, Greece) demonstrated that biopitting is always found in connection with microcolonies of dematiaceous fungi, which penetrate the rock and form colonies on and in the rock. Based on these field observations and the laboratory experiments, a model for the mechanical attack of rock by dematiaceous fungi is proposed.