Tertiary bioreceptivity of Hontoria limestone treated with secondary metabolites

Comunicación presentada en The Second International Congress on Science and Technology for the Conservation of Cultural Heritage was held in Seville, Spain, June 24-27, 2014

Sedimenlary rocks, and in particular, limeslone have been exlensively used in the Mediterranean Basin for the construction of monuments and hisloric buildings. In spite of its reputation of "eternal", limestone is not immune to weathering factors, such as biological decay or biodeterioration. Moreover, the high receptivity of the fragile calcium carbonate matrix results in a progressive deterioralion of the stone material and, over time, in the progressive loss of our cultural heritage. Biocides used lo prevent the growth of micro- and maeroflora responsible for stone biodeterioration are mostly based on the use of chemical methods. Nevertheless, they show restricted efficiency and can eause discolorations on the surtaces and even severe damages to the cultural assets. Recently, the use of natural biocides (derived from living organisms as microorganisms or planls) has attracted particular interest due to their low loxicity, specificily, effecliveness using small dose and fast decomposition rate when compared to synthetic biocides. The aim of this work is to assess the tertiary bioreceptivity of Hontoria limestone treated with secondary melabolites (organic compounds produced in certain stages of development in microorganisms and in specific parts of plants) lo phototrophic microorganisms. Three natural biocides were selecled: (i) cells free filtrate of bacterium Burkholderia gladioli pv. agaricicola ICMP 11096 strain (Bga); (ii) cells free filtrate of fungus Trichoderma harzianum strain T-22; and (iii) glycoalkaloids extracts from unripe berries of Solanum nigrum (European Black Nightshade), a spontaneous plant belongs to Solanaceae family. During three months of incubalion, spectrophotometric deterrnination of chlorophyll a was monthly pertormed in order to evaluate the total amount of photosynthetie biomass. In addition, the efficiency as biocides of the metabolites tested was assessed by digital image analysis (Principal Components Analysis) for the quantification of surtaee covered areas, and by field emission scanning electron microscopy. Preliminary results revealed that the glycoalkaloids are the mosl efficient biocidal treatment, whereas the Trichoderma harzianum filtrate haslened Ihe development of pholotrophic microorganisms on the stone probes. As a conclusion, the use of natural biocides could be a greater safe and eeo-friendly alternative Ihan most common biocides. They can also be used as a preventive method to minimize biodeterioration and thereafter reduce maintenance interval and costs.

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