Primary bioreceptivity of granitic rocks to phototrophic biofilms. Development of a bioreceptivity index

A comprehensive evaluation of the primary bioreceptivity to phototrophic biofilms of several varieties of granite was carried out. The bioreceptivity of the granites was more strongly affected by the physical characteristics of the stones than by their chemical composition. Growth of phototrophic biofilms was strongly enhanced by high open porosity, capillary water content and surface roughness. The findings of the study enabled us to develop a robust and well-founded bioreceptivity index (BI) for granitic rocks. The proposed BI has two components: BIgrowth, which quantifies the extent of the biological growth, and BIcolour, which quantifies the colour change undergone by the stone due to the colonisation and which can be considered the bioreceptivity perceptible by the human eye. The index was fitted to a qualitative scale of 0-10 and can therefore be used as a decision-making tool for selection of appropriate lithotypes for building and/or ornamental purposes

Effect of Inorganic Carbon Concentration on the Development of Subaerial Phototrophic Biofilms on Granite

Organisms living at the stone–air interface are expected to be affected by changes in the atmospheric composition due to greenhouse gases emissions. Increased CO2 concentrations may particularly affect phototrophic microorganisms that colonize stone cultural heritage and form subaerial biofilms. However, little is known about the effects of the environmental changes on microorganisms that colonize stone and the consequences for cultural heritage conservation. In the present study, we investigated how an increase in inorganic carbon concentration affected the development of a subaerial biofilm composed by the cyanobacterium Synechocystis sp. PCC 6803 grown on granite. For this purpose, we established two experiments on biofilm formation, with and without addition of inorganic carbon to the growth medium. Higher concentrations of carbon promoted biofilm growth and increased the concentrations of the photosynthetic pigments chlorophyll a and carotenoids on granite surface, potentially exacerbating the aesthetic impact of these biofilms on stone-made cultural heritage. However, the extracellular polysaccharides produced were not significantly affected by carbon availability, so that physical stone biodeterioration might not be increased by the cyanobacterial matrix. The findings provide valuable data on how the existing global change scenario might affect organisms inhabiting stone cultural heritage and encourage to develop new sustainable treatments and methodologies to prevent biodeterioration and thus preserve stone cultural heritageThis study was partly financed through project CGL2016-79778-R (AEI/FEDER, UE) and Xunta de Galicia (ED431 2018/32). D. Vázquez-Nion was financially supported by Postdoctoral Fellowship-Contract from Xunta de Galicia (ED481B/2017/016). E. Fuentes was financially supported by a PhD Fellowship-Contract MICINN-FPI (BES-2017-079927)S

Shaping colour changes in a biofilm-forming cyanobacterium by modifying the culture conditions

This is the accepted manuscript of the following article: Prieto, B., Vázquez-Nion, D., Silva, B., & Sanmartín, P. (2018). Shaping colour changes in a biofilm-forming cyanobacterium by modifying the culture conditions. Algal Research, 33, 173-181. doi: 10.1016/j.algal.2018.05.010Cyanobacteria, pioneering microorganisms that create a conditioning layer on substrates and act as a source of nutrients for successive colonization by heterotrophic microbes, are commonly studied in relation to the microbial ecology of stones in indoor and outdoor habitats. They are well known for producing greenish-yellow, bluish-green or occasionally pink or pinkish-orange discolouration of surfaces. Such discolouration may be desirable for integrating new elements in landscapes and could be achieved by inoculating surfaces with cyanobacteria of a specific colour. In the present study, with the aim of producing cultures of perceptibly different hues, we modelled the colourimetric response of the biofilm-forming cyanobacterium Nostoc sp. PCC 9104 to variations in light intensity (L) and the concentrations of phosphorus (P) and nitrogen (N). The model obtained, which was validated from both mathematical and perceptual perspectives, enables production of cultures of a particular hue, within a range of 18° and with an efficacy of 92%. Coloured cultures of hue between 129° and 147°, corresponding to yellowish-green to bluish-green tones, were obtained by modifying nutrients inputs and the amount of light, without the need to resort to genetic manipulationThis study was partly financed through grant GRC2014/028 (Xunta de Galicia) and project CGL2016-79778-R (Ministerio de Economía, Industria y Competitividad). D. Vázquez-Nion is financially supported by a postdoctoral contract ED481B/2017/016 (Xunta de Galicia). P. Sanmartín is financially supported by a postdoctoral contract POS-B/ 2016/030 (Xunta de Galicia). The authors thank all the observers who generously agreed to collaborate in the psychophysical studyS

Conversion of a digital camera into a non-contact colorimeter for use in stone cultural heritage: The application case to Spanish granites

In this study, a digital CMOS camera was calibrated for use as a non-contact colorimeter for measuring the color of granite artworks. The low chroma values of the granite, which yield similar stimulation of the three color channels of the camera, proved to be the most challenging aspect of the task. The appropriate parameters for converting the device-dependent RGB color space into a device-independent color space were established. For this purpose, the color of a large number of Munsell samples (corresponding to the previously defined color gamut of granite) was measured with a digital camera and with a spectrophotometer (reference instrument). The color data were then compared using the CIELAB color formulae. The best correlations between measurements were obtained when the camera works to 10-bits and the spectrophotometric measures in SCI mode. Finally, the calibrated instrument was used successfully to measure the color of six commercial varieties of Spanish granite.The present study was financially supported by the Xunta de Galicia (09TMT014203PR) and the European Union and Spanish Ministry of Economy and Competitiveness under grants DPI2008-06455-C02-02 and DPI2011-30090-C02-02. Dr. Patricia Sanmartín acknowledges a scholarship for postgraduate studies abroad (2012 Call) from Barrié de la Maza Foundation. She is currently supported by a postdoctoral contract within the framework of the 2011–2015 Galician Plan for Research, Innovation and Growth (Plan I2C) for the year 2012

Acidification of mixtures of granite powder and compost for reuse in plant production

We evaluated the utilization of granite powdera residue of stone cutting and polishing resulting from its preparation for construction and ornamental usein the preparation of nursery potting mixtures, within a general objective of waste recycling and reuse. Granite powder was blended with two composts of different origins and properties: one elaborated from the organic fraction of municipal solid waste (MSW), and another from pine bark. Since all materials presented pH values over 8, which are excessive for growing most vegetal species, the use of iron sulphate to acidify them has been assessed. Three doses of iron sulphate (14, 69, and 97g kg(-1), equivalent to 0.1, 0.5, and 0.7 meq H+ g(-1)) were added to the granitic powder and mixtures with 25 or 75% (v/v) of each compost, which were incubated in the laboratory during 30days. Doses of iron sulphate above 0.1 meq H+ g(-1) resulted in excessive electrical conductivity (>2 dS m(-1)) in all the samples, and too low pH values (<5) in most of them. The productivity of granite powder/compost mixtures acidified with 0.1 meq H+ g(-1) was tested in a greenhouse experiment with ryegrass, where it was observed that plant productivity increased with respect to a control commercial substrate based on peat, in particular when the MSW compost was employed. On the basis of the physicochemical properties of the mixtures and the results of the greenhouse experiment, the use of granite powder mixed with 75% of MSW compost (v/v), acidified with 14g kg(-1) of iron sulphate (0.1 meq H+ g(-1)) is recommended