Primary bioreceptivity: A comparative study of different Portuguese lithotypes

The current condition of many historical monuments clearly reveals that they are not immune to “weathering” factors such as biological decay or biodeterioration. In the present study, Portuguese lithotype samples were inoculated in the laboratory with the microalga Stichococcus bacillaris and the cyanobacterium Gloeocapsa alpina in order to study their primary bioreceptivity and to establish an index of bioreceptivity. The types of building stones used were Ançã and Lioz limestone, Portalegre granite and Vila Viçosa white marble, which are materials renowned in Portuguese architecture. Microbial growth, including the area of the stone surface covered, was evaluated by visual examination and measurement of in vivo chlorophyll a fluorescence using a spectrofluorometer fitted with a fibre-optic accessory. It was possible to verify that 4 months after inoculation, colonization had led to development of biofilms similar to those occurring on stone monuments located outdoors. The results showed that Ançã limestone had the highest primary bioreceptivity, followed by Lioz limestone, with Portalegre granite being weakly colonized or not colonized at all. White marble was not taken into account for the bioreceptivity index, since ANOVA results of microbial growth showed greater internal variance among replicates than between these and the other lithotypes.