9 páginas.-- 5 figuras.-- 1 tabla.-- 73referencias.--Rocks, either in natural geological outcrops or in stone monuments, are common habitats for a wide variety of microorganisms which colonize both rock surfaces and cracks. Physical properties such as porosity and surface roughness make limestone susceptible to biological colonization, which may induces aesthetic and/or physical and chemical damages. Organisms causing biodeterioration on monuments have usually been controlled by chemical products (biocides). In order to overcome the impact of these substances on the environment, human health and stone substrates, alternative tools such as natural products from plants or microorganisms can be used as an innovative approach for stone conservation.\ud In this work, the efficiency of natural biocides (cells free culture filtrates of Trichoderna harzianum and Burkholderia gladioli, as well as glycoalkaloids from spontaneous Solanaceae) was tested under laboratory conditions against a multi-species phototrophic culture developing on Hontoria limestone. Their efficiency was assessed by digital image analysis, in vitro chlorophyll a quantification and confocal laser scanning microscopy. These techniques showed a good correlation, revealing that cells free filtrate of Trichoderma harzianum had an antagonistic action against the multi-species phototrophic culture tested in this work.S. Sasso acknowledges the opportunity to carry out a predoctoral stay at IRNAS-CSIC. A.Z. Miller acknowledges the support from the Marie Curie Intra-European Fellowship of the European Commission's 7th Framework Programme (grant: PIEF-GA-2012-328689).Peer reviewe

Different Mediterranean Basin limestones, like Calcário Ançã (Portugal), Calcário Lioz (Portugal), Piedra San Cristobal (Spain), Piedra Escúzar (Spain) and Pietra di Lecce (Italy), have been widely used as building materials in the European architecture. The aim of this study was focused on biodeterioration, mainly on evaluation of the primary bioreceptivity of those materials. A set of samples was inoculated with a cultured photosynthetic biofilm under laboratory conditions. Several assessment tools were applied to monitor the colonization overtime of the different lithotypes. After 3 months of incubation the colonization occurred endolithically in some lithotypes, namely Piedra San Cristobal and Piedra Escúzar . Spectrophotometric determination of chlorophyll a was a useful analytical technique to achieve the total amount of photosynthetic biomass on rock substrates, demonstrating that Piedra Escúzar and Calcário Lioz were the highest and lowest bioreceptive lithotypes, respectively. Microscopic and image analyses were essential to understand the stone colonization process and its pattern of distribution. Physical stone parameters and exposure conditions were shown to play an important role in the establishment and development of photosynthetic colonization.