Relationship between color and pigment production in two stone biofilm-forming cyanobacteria (Nostoc sp. PCC 9104 and Nostoc sp. PCC 9025).

Previous studies have provided evidence that color measurements enable on site quantification of superficial biofilms, thereby avoiding the need for sampling. In the present study, the efficiency of color measurements to evaluate to what extent pigment production is affected by environmental parameters such as light intensity, combined nitrogen and nutrient availability, was tested with two cyanobacteria, Nostoc sp. strains PCC 9104 and PCC 9025, which form biofilms on stone. Both strains were acclimated, in aerated batch cultures for 2 weeks, to three different culture media: BG-11, BG-11(0), and BG-11(0)/10 at either high or low light intensity. The content of chlorophyll a, carotenoids, and phycocyanins was measured throughout the experiment, together with variations in the color of the cyanobacteria, which were represented in the CIELAB color space. The results confirmed that the CIELAB color parameters are correlated with pigment content in such a way that variations in the latter are reflected as variations in color.

Recycling of waste products in the induction of biofilms to remediate the visual impact generated by quartz mining.

The present study was undertaken to investigate the viability of the use of two waste products, cheese whey and composted organic waste, as nutrient sources in the induction of biological films on quartz surfaces, with the final aim of reducing the visual impact generated by quartz mining. Experiments were carried in laboratory in which quartz samples were colonized with microorganisms (mainly cyanobacteria) forming biofilms. Previous studies have shown that a nutritional supplement must be added for good development of biofilms and, therefore, application of the two waste products was compared with application of the chemical nutrient medium on which these types of microorganisms are usually cultivated. Both products provided better results than the culture medium, in terms of the speed of formation of the biofilm, faster with the waste products, and the degree of cover of the brilliant white colour of the quartz, better masked by the biofilms formed when the waste products were applied as a darker biofilm was obtained.

Comparative study of dark patinas on granitic outcrops and buildings.

Formation of dark patinas on rocky surfaces is mainly related to the deposition of gases and particles and to sulphation mechanisms. In the present study, samples of dark patinas taken from granitic outcrops and from granitic buildings were examined in an attempt to understand the mechanisms of their formation. The outcrops are located in non-polluted areas and are characterized by the absence of any extraneous material that provides calcium, such as e.g. mortar. The buildings are located in areas with low levels of pollution. The climate in the study area favours proliferation of microorganisms. Important differences between the patinas sampled from outcrops and from buildings were observed, as the former are of biological origin and the latter of anthropogenic origin. Although the levels of pollution are low in the sampling area, sulphur was present in all of the samples from urban buildings. Sulphur was not present in patinas from outcrops or in patinas from monuments that are assumed to behave as outcrops (dolmens), although the latter are also of anthropogenic origin. Finally, the patinas were found to be formed by elements accumulated on the surface and not from elements contained within the rock itself.

Gas chromatography applied to cultural heritage. Analysis of dark patinas on granite surfaces.

The formation of dark patinas has been mainly related with deposition of gases and particles, and sulphation mechanisms particularly in calcareous rocks. However, in granitic monuments located in Galicia (northwest of Spain), especially in rural areas, this origin is unlikely since granite is a very poor calcium-containing rock and the atmospheric pollution in this area is negligible. A biological origin seems to be most probable. In order to know the importance of biological and atmospheric factors in the formation of dark patinas on granitic monuments, a number of analyses using several techniques are needed. The characterization of fatty acids in patinas by gas chromatography has established clear differences among samples. Thus, all of the samples having a biological origin displayed a similar fatty acid pattern, with unsaturated fatty acids predominating, especially oleic and linoleic acids; these were followed in abundance by the branched fatty acid 18:00 anteiso, and palmitic acid. Different patterns of fatty acid allowed establishment of an anthropogenic origin of the some of the patinas analysed.

Methodological aspects of the induction of biofilms for remediation of the visual impact generated by quartz mining.

The opening up of mine faces causes severe alteration to the environment that must be remedied. In the case of quartz mines, the bright white colour of the mineral gives rise to a significant impact that is visible for long distances. New techniques to correct this visual impact, based on the induction of biofilms on the faces, have recently been developed in an attempt to imitate natural effects that mask the impact. Although techniques have been applied successfully in the laboratory, they must be optimized to ensure their success in the field. In the present study, the results of a randomized factorial experiment indicated that although the biofilms adhere to the faces naturally, without the use of adhesives, continued development of the film depends to a large extent on the input of nutrients. Water must also be provided with nutritional supplement to maintain the required level of moisture.

Induction of biofilms on quartz surfaces as a means of reducingthe visual impact of quartz quarries.

In the present study the induction of biofilms on the open rock faces of quartz quarries is reported as a feasible method of correcting the visual impact generated by the industry. Experiments were carried out to colonize quartz samples with microorganisms isolated directly from aged quarry faces. The results demonstrated the viability of inducing colonisation on quartz, which is not the most favourable material for such treatment. Furthermore, biofilm development caused a significant change in the colour of the surface of the quartz samples to greenish- or reddish yellow, which may be quantified by a colorimeter for solids. The notable change in the colour is sufficient to attenuate the bright white aspect of the quartz faces and therefore to correct the visual impact generated.