Piero Tiano

Biodiversity of photosynthetic micro-organisms dwelling on stone monuments

A critical survey of literature data for the biodeteriogens acting on stone monuments was combined with the results of our investigations performed by traditional and biomolecular (ARDRA) methods. It was showed that the photosynthetic micro-organisms dwelling on stone monuments have a rather ample biodiversity, and this was also confirmed by our data on axenic cyanobacterial strains isolated from Italian monuments. The correlation between the literature data reporting the presence of photosynthetic micro-organisms, and the nature of the stone substrate showed that the cyanobacteria Chroococcus, Myxosarcina, Pleurocapsa and Scytonema, and the chlorophyta Apatococcus and Stichococcus were associated with calcareous substrates, while Nostoc spp. were more frequently associated with artificial substrates. We also demonstrated that Lyngbya B2 and Apatococcus B4, isolated from monuments inoculated on stone slabs differing in porosity and surface roughness, had a preference for calcareous lithotypes with high values of roughness and porosity.

Standardization of peeling tests for assessing the cohesion and consolidation characteristics of historic stone surfaces

A peeling test known as the “Scotch Tape test” has been used for more than 40 years in conservation practice for assessing the consolidation efficiency of degraded stone. However, the method has not been supported by any standard or reliably verified recommendations for its application. Its applicability is overestimated, and its unrestricted use without adequate knowledge and sufficient understanding can lead to non-comparable, non-reproducible and, in many cases, incorrect and severely biased results and assessments. This paper presents the results of a recent study focused on establishing limits for application, reliable procedures and a “standard” protocol for testing the cohesion characteristics of brittle and quasi-brittle materials, mainly mortars and stones. The main application strategy exploits repeated peeling in the same place on a surface in order to eliminate the effect of the natural decrease in the detached material from the subsurface layers, which might be incorrectly interpreted as a consolidation effect. There is a discussion of factors influencing the performance of the peeling test method, and examples of peeling measurements on various natural and artificial stones are presented.

Biodeterioration of ornamental marble statues in the Boboli Gardens (Florence, Italy)

The colonisation of ornamental marble statues in theBoboli Gardens of Florence (Italy) by photosyntheticmicro-organisms was investigated. The greenmicroalga Coccomyxa was the first colonizer ofnewly restored marble surfaces, appearing one yearafter the periodic cleaning and restoration of thestatues. Two years after restoration this alga gaverise to very thin green biofilms, with densitiesreaching about 3 × 102 cells cm-2. Later,the biofilms were enriched by cyanobacterial forms,which became dominant. In about six years, aphotosynthetic microbial community, amounting to about3 × 104 cells cm-2, and structurally similarto that occurring on the unrestored statues wasdeveloped. This epilithic community showed amarked biodiversity; the main representative formsincluded Chroococcidiopsis, Leptolyngbya,Pleurocapsa, Coccomyxa and Apatococcus.Coccomyxa initiated the colonisation of themarble surfaces, favoured in this process by itsfacultative oligotrophic capacity and high cellsurface hydrophobicity, combined with tolerance ofhigh light intensity. The other investigated isolatedstrains did not show this set of features. Thesecretion of polysaccharidic substances and cellsurface hydrophobicity enhancing the capacity toadhere, favoured permanent colonisation of thecyanobacterial population. Indeed, the majority of thecyanobacterial strains (90%), were shown to besurrounded by exopolysaccharidic envelops, whichcontributed to the formation of stable microbialbiofilms, and possessed variable cell surfacehydrophobicity.

Biodiversity of Phototrophic Biofilms Dwelling on Monumental Fountains

Among the stone monumental assets, artistic fountains are particularly affected by microbial colonization due to constant contact with water, giving rise to biodegradation processes related with physical–chemical and aesthetical alterations. In this paper, we make an overview of reported biodiversity of the phototrophic patina developed in various fountains of Italy and Spain. The microbial composition of four fountains (two from Florence, Italy and two from Granada, Spain) was investigated using traditional and/or molecular techniques. The results indicated many common similarities with regard the phototrophic biodiversity for all the investigated fountains. Automated ribosomal RNA intergenic spacer analysis (ARISA), a molecular fingerprint tool, was used to examine the eubacterial and cyanobacterial community for two of the investigated fountains. The principal component analysis of ARISA profiles strengthens the results obtained by traditional methods and revealed separate clusters, as a consequence of the differences of micro-environmental conditions for each fountain.

Experiments on stony monument monitoring by laser-induced fluorescence

Abstract The use of remote sensing techniques for the monitoring of historical buildings is attractive, since it can allow a fast monitoring of large surfaces without the use of scaffolding and, in addition, a thematic mapping which is easier to read. The studies on fluorescence lidar monitoring of buildings started a few years ago and are still in progress. Interesting results were obtained in biodeteriogen monitoring and in the identification of stones. The possibility of detecting fluorescence thematic images of large areas was demonstrated on both artificial targets and historical buildings. This paper describes the current state of the art on fluorescence lidar monitoring of buildings and the research trends for the near future.

Lidar remote sensing of stone cultural heritage: detection of protective treatments

Treatments utilizing different chemical compositions are employed to preserve the surface of historical stone building. The uniform distribution of the protective treatment and the conservation of its integrity over the years are crucial factors for an efficient protection of monuments. A technique that enables a remote mapping of the treatment and its characteristics is therefore very attractive. We describe the first experiments devoted to the investigation of the potential of fluorescence lidar in monitoring protective treatments on stone surfaces. Dolomitic marble samples are treated with different protective substances, and are then analyzed by a laboratory setup that simulates a lidar measurement. Although further investigations will be necessary, these laboratory results indicate an interesting potential for lidar in the nondestructive, remote monitoring of protective treatments.

Occurrence and Fluctuation in Photosynthetic Biocoenoses Dwelling on Stone Monuments

This research deals with the occurrence and fluctuation of phototrophic microbial communities dwelling on stone monuments. We examined many photosynthetic biocoenoses of several Italian monuments. The most widespread and recurring taxa occurring in the epilithic communities were among the cyanobacteria Chroococcidiopsis, Pleurocapsa, Leptolyngbya and Plectonema, and among the chlorophytes were Coccomyxa, Apatococcus, Chlorococcum and Stichococcus. The community composition was subjected to small seasonal changes affecting the amounts of the different components more than the qualitative biocoenosis structure. The number of phototrophic microorganisms increased slightly from late spring to autumn, in accordance with the improvement of climatic conditions. In winter and early spring, we found the lowest amount of phototrophic microorganisms. A detailed study, carried out on marble statues in the Boboli Garden (Florence, Italy), showed that the first coloniser was the green alga Coccomyxa. We observed that stone colonisation started about one year after restoration. The success of Coccomyxa in marble stone colonisation could be attributed to its specific growth strategy and features.

Detection and characterization of biodeteriogens on stone cultural heritage by fluorescence lidar

Biodeteriogens are an important cause of the weathering of a monument, particularly those made of stone, and their detection at an early stage of development helps to protect the monument from deterioration. Frequent mapping of biodeteriogen accumulation is therefore highly necessary. The use of fluorescence lidar for this purpose was introduced in 1995 and has been developed in subsequent years. Three main aspects emerged during this research: the possibility of discriminating between different biodeteriogen strains, the minimum detectable quantity of biodeteriogens, and the control of the efficiency of biocide treatments. We describe the results of a laboratory experiment devoted to clarifying these three aspects of biodeteriogen monitoring by means of fluorescence lidar.

Bacterial Genes Involved in Calcite Crystal Precipitation

The natural precipitation of calcium carbonate crystals by bacteria has been proposed for conservative interventions in monument restoration, even if the use of heterotrophic viable organisms does not always seem appropriate for this purpose. In fact, chemical reactions with stone minerals due to metabolic by-products and the growth of fungi, due to the application of organic nutrients for bacterial development, can have negative effects on stone surfaces. We have studied crystal precipitation in a laboratory strain of Bacillus subtilis. The effectiveness of this process has been analyzed on small bioclastic limestone samples (Pietra di Lecce), determining their total porosity, amount of water absorbed and superficial cohesion. To overcome some of the possible problems involved with the use of viable bacterial cells, we have investigated the genetic mechanisms that control calcite precipitation. For this reason, we have selected Bacillus subtilis mutants that do not precipitate or which form calcite crystals faster. The data obtained suggest the presence of several genes involved in crystal formation.

Alternative nutrient sources for biotechnological use of Sporosarcina pasteurii.

The potential use of Sporosarcina pasteurii in possible biotechnological applications on a large scale (ground improvement, consolidation of building structures and ornamental stone, or in developing bio-materials for the building industry), is based on its ability to produce high amounts of carbonate in a short period of time via urea hydrolysis. Industrial biomass production would have a low environmental impact and would be most economical if the standard growth media could be replaced with alternative nutrient sources, such as byproducts or wastes from other industries, or other low cost ingredients. The use of cost effective ingredients must guarantee ureolytic activities and growth conditions that are comparable to those resulting from the standard nutrient medium. In this work, three types of alternative media were tested for growing the ureolytic active bacteria S. pasteurii: (1) alternative nutrient sources such as industrial wastes resulting from the dairy and brewery industries, (2) fertilizer urea as an alternative urea substitute, and (3) different types of poultry manure based fertilizers as nutrient and urea substitutes. The comparison between the standard media, the nutrient alternatives and urea substitutes was possible by taking the protein concentration and nitrogen content into account. Bacterial activity was evaluated in terms of biomass changes over time (CFU, optical density, ATP measurements) and indirect estimation of the enzyme production (Nessler assay, conductivity measurement). The results revealed that some of the dairy wastes tested, such as whey and buttermilk, are potential alternative nutrients for bacterial development, while the urea fertilizer is perfectly suitable as an economical substitute for pure laboratory grade urea.