LICHENIZED ASSOCIATION BETWEEN SEPTONEMA TORMES SP. NOV., A COCCOID CYANOBACTERIUM, AND A GREEN-ALGA WITH AN UNFORESEEN BIOPRESERVATION EFFECT OF VILLAMAYOR SANDSTONE AT CASA-LIS OF SALAMANCA, SPAIN

'Casa Lis' is the most characteristic building in Salamanca, Spain, be longing to the modernist trend. It was built with Villamayor sandstone from nearby Salamanca, which has high porosity providing an easy medi um for water absortion and capillarity. During a restoration process o n the southern wall, near an underground water flow, two well defined, naturally developed layers were observed on the sandstone surface: an outer, hard crust with greyish shades and whitish salt patches result ing from rising damp, and an inner, green layer with organic material linking the sandstone to the inorganic crust. The microbiological stud y of this biofilm showed an ecologically obligate, stable mutualism be tween a dematiaceous mitosporic fungus (Septonema tormes sp. nov.), a coccoid cyanobacterium (Cyanothece-group) and a green alga (Gloeocysti s rupestris), with the accumulation of different metabolites excreted by these microorganisms. The case reported here is one of the few stud ies where a microbial mat, in association with the external crust, avo ids a further weathering of the stone because of an unforeseen biopres ervation-effect due to the maintenance of humidity at constant levels under the crust avoids changes in clay swelling and subsequent surface arenization of the sandstone. The lichenized complex of a mitosporic mycobiont and two photobionts, in this case, has not been reported bef ore as a stable association on this kind of substrate.