PRIMARY BIO RECEPTIVITY UNDER LABORATORY-CONDITION ON DIFFERENT LIMESTONE WIDELY USED IN THE CONSTRUCTION OF HISTORIC MONUMENTS IN SOUTH ITALY

Weathering of natural stones exposed to the atmosphere is caused by a combination of physical, chemical, and biological processes. Several investigations during the last 10-15 years have made it apparent that, in addition to chemical weathering, microbiologically induced weathering contributes to the deterioration of building stones. All types of building material are colonisable by microorganisms, because it is virtually impossible to protect rocks or buildings from bacteria, fungi and microalgae in the natural environments. In particular, the fungal growth on stone surfaces is responsible not only of aesthetic deterioration due to the production of pigments and organic acids that can stain or damage the stone, but it is also responsible of the subsequent structural deterioration because of the hyphal growth through the rock material that increases the porosity of stone, favouring in the long time the settlement also of higher plants. Guillitte in 1995 has introduced the concept of “Bio-receptivity” explaining it as «the aptitude of a material to be colonised by one or several groups of living organisms». “Bio-receptivity” can also be defined as the totality of material properties such as roughness, porosity, moisture and the chemical composition of the surface layer that, exposed in particular environmental conditions, allows the establishment, anchorage and development of microorganisms. The aim of this work is to test the receptivity to the fungal colonization of three different building stones (Lecce, Canosa and Grottaglie). All sterile materials were inoculated under controlled environmental conditions with several species of fungi isolated previously from historical deteriorated surfaces in order to reproduce the natural colonization. Samples were successively exposed to natural solar light in aseptic conditions to avoid unwanted contaminations and to understand the time of degradation exclusively due to inoculated fungi. Petrographic investigation, and Scanning Electron Microscopy (SEM) showed an elevated bio- receptivity of Grottaglie and Canosa stones more porous than Lecce stones that have different physical and chemical properties.