INSTITUTO DE RECURSOS NATURALES Y AGROBIOLOGÍA DE SEVILLA (IRNAS-CSIC)

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

This study is aimed to assess the formation of photosynthetic biofilms on and within different natural stone materials, and to analyse their biogeophysical and biogeochemical deterioration potential. This was performed by means of artificial colonisation under laboratory conditions during 3 months. Monitoring of microbial development was performed by image analysis and biofilm biomass estimation by chlorophyll extraction technique. Microscopy investigations were carried out to study relationships between microorganisms and the mineral substrata. The model applied in this work corroborated a successful survival strategy inside endolithic microhabitat, using natural phototrophic biofilm cultivation, composed by cyanobacteria and algae, which increased intrinsic porosity by active mineral dissolution. We observed the presence of mineral-like iron derivatives (e.g. maghemite) around the cells and intracellularly and the precipitation of hausmannite, suggesting manganese transformations related to the biomineralisation.

The influence of open porosity, water absorption capillarity, water vapour permeability, surface roughness, stone pH and chemical composition on stone bioreceptivity to phototrophic microorganisms was assessed by means of a thorough stone characterisation with subsequent artificially inoculation of limestone samples with a multi-species phototrophic culture and placing them inside a growth chamber for 90 days. A principal component analysis and an analysis of variance (ANOVA) were carried out in order to evaluate the direct relationships between stone bioreceptivity and petrophysical properties. From the principal component analysis, two main components were obtained and assigned a petrophysical/photosynthetic biomass meaning. Stone bioreceptivity, quantified by the amount of chlorophyll a and intensity of chlorophyll a fluorescence present on the stone samples after 90 days-incubation, was included in both principal components. The first component was linked to the amount of chlorophyll a and was highly and linearly associated to capillarity and roughness, and less associated with open porosity and water vapour permeability. The second component, linked to the intensity of chlorophyll a fluorescence measured on the stone surfaces, was not linearly associated with the petrophysycal properties, showing the fallibility of this in vivo chlorophyll quantification technique on the estimation of photosynthetic biomass growing on stone materials, particularly when endolithic growth occurs.

In the last few years, the microbial colonisation of mural paintings in ancient monuments has been attracting the attention of microbiologists and conservators. The genus Rubrobacter is commonly found in biodeteriorated monuments, where it has been reported to cause rosy discolouration. However, to date, only three species of this genus have been isolated, all from thermophilic environments. In this paper, we studied three monuments: the Servilia and Postumio tombs in the Roman Necropolis of Carmona (Spain), and Vilar de Frades church (Portugal), in search of Rubrobacter strains. In all cases, biodeterioration and the formation of efflorescences were observed, and five Rubrobacter strains were isolated. These isolates showed different physiology and migration in denaturing gradient gel electrophoresis, suggesting they might represent new species within this genus. The isolates reproduced some biodeterioration processes in the laboratory and revealed their biomediation in crystal formation.

Biological colonisation of stone is one of the main problems related to monuments and buildings conservation. It is amply recognised that microalgae have the greatest ecological importance as pioneer colonisers of stone materials, conducting to aesthetic, physical and chemical damages. Their deterioration potential is related with their photoautotrophic nature, using the mineral components of stone substrates and sunlight as energy source without any presence of organic matter. Stone biodeterioration by microalgae has been assessed ...

ABSTRACT Coralloid-type speleothems were recorded on the ceiling of the Ana Heva lava tube in Easter Island (Chile). These speleothems were morphologically, geochemically and mineralogically characterized using a wide variety of microscopy and analytical techniques. They consist dominantly of amorphous Mg silicate and opal-A. Field emission scanning electron microscopy revealed a variety of filamentous and bacillary bacteria on the surface of the Ana Heva coralloid speleothems, including silicified filamentous microorganisms. Among them, intriguing reticulated filaments resemble those filaments documented earlier in limestone caves and lava tubes. The identification of silicified microorganisms on the coralloid speleothems from the Ana Heva lava tube suggests a possible role of these microorganisms in silica deposition.