Detection of endolithic spatial distribution in marble stone

Summary: The penetration of endolithic microorganisms, which develop to depths of several millimetres or even centimetres into the stone, and the diffusion of their extracellular substances speeds up the stone deterioration process. The aim of this study was to investigate, using a confocal laser scanning microscopy with a double-staining, a marble rock sample by observing the endolithic spatial distribution and quantifying the volume they occupied within the stone, in order to understand the real impact of these microorganisms on the conservation of stone monuments. Often the only factors taken into account by biodeterioration studies regarding endolithic microorganisms, are spread and depth of penetration. Despite the knowledge of three-dimensional spatial distribution and quantification of volume, it is indispensable to understand the real damage caused by endolithic microorganisms to stone monuments. In this work, we analyze a marble rock sample using a confocal laser scanning microscopy stained with propidium iodide and Concavalin-A conjugate with the fluorophore Alexa Fluor 488, comparing these results with other techniques (SEM microscope, microphotographs of polished cross-sections and thin-section, PAS staining methods), An image analysis approach has also been applied. The use of confocal laser scanning microscopy with double staining shows clear evidence of the presence of endolithic microorganisms (cyanobacteria and fungi) as well as the extracellular polymeric substance matrix in a three-dimensional architecture as part of the rock sample, this technique, therefore, seems very useful when applied to restoration interventions on stone monuments when endolithic growth is suspected

DIFFERENTIAL EFFECTS OF TREATMENTS ON THE DYNAMICS OF BIOLOGICAL RECOLONISATION OF TRAVERTINE: CASE STUDY OF THE TIBER’S EMBANKMENTS (ROME, ITALY)

Monuments exposed to the environment are subject to numerous causes of degradation, including the action of biological organisms forming patinas and crusts of various colour and different aggressiveness. However, these patinas can be used in contemporary art for the creation of drawings, as in William Kentridge’s project, along the embankment of the Tiber River, illustrating the “Triumphs and Laments” of Rome history. More than eighty figures will be created through selective cleaning of the black biological patina on travertine, which is much used in Rome but little studied in biocide tests. The aim of this study is to understand which chemical treatments could delay the biological growth in the cleaned area, extending the lifetime of the images. Three commercial biocides (Algophase®, Biotin R®, Preventol R80®) and two water-repellents (Hydrophase superfici®, Silo 111®) were chosen and tested in situ (30 tests areas, with three repletion) using different concentrations and mixtures, in accord with the safety of users and environment. In order to limit the re-colonization after treatments, colour measurements and portable optical microscope were conducted both on the bare surface of the stone (the control test) and on the stone after chemical treatments.The results show that each product has different biocidal efficacy and a different colorimetric response. The preventive treatment of Preventol R80® with subsequent application of biocides in mixture had the best results in preventing re-colonisation. The use of water repellents alone was revealed to be ineffective in preventing biological recolonization and also determined colorimetric alterations in terms of brightness.The experimental data has provided an improved understanding of the effects of chemical treatments on travertine and of the phenomena of biological recolonization dynamics

Pink patinas and incrustations in tropical environment: Phnom Krom temple case (Angkor, Cambodia)

The formation of pigmented patinas and encrustations on stone monuments, connected to chemical or biological deterioration, can give rise to aesthetic alterations. Pink patinas related to biodeterioration phenomena have been widely observed throughout Europe and in tropical climates, like on the Khmer temple of Bayon (Angkor, Cambodia) or Mayan monuments in Uxmal (Mexico). They generally occur under specific environmental conditions, such as interior or semi-confined areas with specific lighting conditions, a high saline content and substantial variations in humidity and temperature. Other pink discolorations can be observed in the morphology of hard encrustations on the sandstone of one of the buildings of Phnom Krom temple. They occur on exterior surfaces characterised by different conditions than those of the pink alterations at Bayon. Considering their unclear origin and unusual morphology, this paper aims to characterise them and define their chemical or biological origin. The observation of fresh slides, fracture samples and cross-sections with optical and SEM/EDS microscopes shows the presence of very small coccoid cells (0.5 μm) surrounded by an extracellular matrix. SEM-EDS analysis highlighted the presence of Si, Fe, Mg, Ca, Na, K associated with the substrate. Phosphorus, aluminium and a small amount of silicon were detected in correspondence with the body of the patina. The high level of P at the Phnom Krom temple can be traced to salts efflorescence originating in bat guano deposits. It seems necessary to hypothesize the simultaneous presence of other phenomena in order to explain the origin of these encrustations. Microscopic observations have shown a microbiological colonization corresponding to P accumulation, arising, at first, from the guano and then mobilised by wet-dry cycles in areas exposed to direct sunlight. The presence of microorganisms seems able to explain this peculiar coloration, but biomolecular analysis will be needed to understand the precise taxonomy of such bacteri

Unusual differential erosion due to endolithic microorganisms on limestone (Martvili, Georgia).

The presence of a diffuse biodeterioration phenomena can be observed across large areas of the outersurface of the limestone walls of the Church of the Virgin in Martvili. A differential erosion phenomenonwas detected, suggesting a possible association with biological colonization. The erosion phenomenon ischaracterized by a circular discoloration leading progressively to the detachment of flakes of limestoneat its center. Since the aforementioned process has not been described in the literature until now, thepresent study was focused on the interpretation of its origin and evolution. Three sides of the Churchare affected by a variety of occurrences of circular differential erosion which display different stages ofthe process, whereas the western side is affected by epilithic growths across its entire surface. Surveysof the petrographic, mineralogical and physical features of the stone were made, and parameters suchas density and porosity were recorded. Samples were analyzed by optical microscopy and SEM analysisin order to detected the presence of microorganisms whose species were then identified by means ofmorphological and molecular examinations. The study of cross-sections stained using the PAS methodhas confirmed the causal connection between microorganisms and the deterioration phenomena, pro-viding information about their spread of penetration into the substrate and their substantial potentialfor causing damage. Dryness appears to be the main ecological condition favoring endolithic rather thanepilithic growth. The most common isolated microorganisms were cyanobacteria (Chroococcales) and,to a lesser extent, meristematic fungi. The characteristics of the stone, and especially some endogenousdiscontinuities related to the accumulation of sedimentary layers and to the action of stone carving tools,might explain why the same differential erosion phenomenon occurs in specific areas of the block stones.The development of the differential erosion phenomenon shows a variety of stages of biological colo-nization. The progressive evolution of the deterioration process has been observed in detail: (a) firstly,white circular discolorations appear on the stone, which darken over time eventually becoming almostblack; (b) circular perforations appear around the perimeter; (c) and finally a flake detaches from thecenter, leaving a deep depression in the stone