Bioreceptivity index for granitic rocks used as construction material

Fungal biodeterioration and preservation of cultural heritage, artwork, and historical artifacts: extremophily and adaptation

SUMMARYFungi are ubiquitous and important biosphere inhabitants, and their abilities to decompose, degrade, and otherwise transform a massive range of organic and inorganic substances, including plant organic matter, rocks, and minerals, underpin their major significance as biodeteriogens in the built environment and of cultural heritage. Fungi are often the most obvious agents of cultural heritage biodeterioration with effects ranging from discoloration, staining, and biofouling to destruction of building components, historical artifacts, and artwork. Sporulation, morphological adaptations, and the explorative penetrative lifestyle of filamentous fungi enable efficient dispersal and colonization of solid substrates, while many species are able to withstand environmental stress factors such as desiccation, ultra-violet radiation, salinity, and potentially toxic organic and inorganic substances. Many can grow under nutrient-limited conditions, and many produce resistant cell forms that can survive through long periods of adverse conditions. The fungal lifestyle and chemoorganotrophic metabolism therefore enable adaptation and success in the frequently encountered extremophilic conditions that are associated with indoor and outdoor cultural heritage. Apart from free-living fungi, lichens are a fungal growth form and ubiquitous pioneer colonizers and biodeteriogens of outdoor materials, especially stone- and mineral-based building components. This article surveys the roles and significance of fungi in the biodeterioration of cultural heritage, with reference to the mechanisms involved and in relation to the range of substances encountered, as well as the methods by which fungal biodeterioration can be assessed and combated, and how certain fungal processes may be utilized in bioprotection.

Biomineral deposits and coatings on stone monuments as biodeterioration fingerprints

Biominerals deposition processes, also called biomineralisation, are intimately related to biodeterioration on stone surfaces. They include complex processes not always completely well understood. The study of biominerals implies the identification of organisms, their molecular mechanisms, and organism/rock/atmosphere interactions. Sampling restrictions of monument stones difficult the biominerals study and the in situ demonstrating of biodeterioration processes. Multidisciplinary works are required to understand the whole process. Thus, studies in heritage buildings have taken advantage of previous knowledge acquired thanks to laboratory experiments, investigations carried out on rock outcrops and within caves from some years ago. With the extrapolation of such knowledge to heritage buildings and the advances in laboratory techniques, there has been a huge increase of knowledge regarding biomineralisation and biodeterioration processes in stone monuments during the last 20 years. These advances have opened new debates about the implications on conservation interventions, and the organism's role in stone conservation and decay. This is a review of the existing studies of biominerals formation, biodeterioration on laboratory experiments, rocks, caves, and their application to building stones of monuments.

The Role of Lichens, Mosses, and Vascular Plants in the Biodeterioration of Historic Buildings: A Review

Biodeterioration is defined as the alteration of a given substrate due to a combination of physical and chemical factors produced by living organisms when attached to such materials. This phenomenon attracts scientific research attention due to its risk in causing destruction to outdoor cultural rock heritage sites. In this review, an update on the state-of-art regarding the biodeterioration phenomenon is represented in order to highlight the type of colonizing vegetation and possible mechanisms behind the corresponding deterioration. For this reason, 62 articles with a focus on lichens, mosses, and higher plants were investigated by evaluating the role of construction materials and different plant species related to the hazard index. The results showed that trees and shrubs are the most harmful plant life forms, for example, Ficus carica, Ailanthus altissima, and Capparis spinosa, while regarding building materials, those characterized by high porosity, such as andesite and argillaceous limestone, are more vulnerable to plant colonization. Further studies are needed to examine in detail the relationship between colonizing organisms, intrinsic elements of the substrate, and external factors, as well as the refinement of measures to prevent and control colonization by plants.

Microstructural, Mechanical and Radiological Characterization of Mortars Made with Granite Sand

The study reported the effect of granite sand on strength and microstructural developments in mortars prepare from OPC with a high coal fly ash (FA) content or from hybrid alkaline cements. The radiological behaviour of the resulting mortars was compared to materials prepared with siliceous sand (with particles sizes of <2 mm) and the relationship between such radiological findings and mortar microstructure and strength was explored. A new method for determining natural radionuclides and their activity concentration Index (ACI) on cement mortars (specifically to solid 5-cm cubic specimens) was applied and validated. The microstructural changes associated in mortars have no effect on mortar radiological content measurements. The mortars with granite sand exhibited very high ACI > 0.96, which would ultimately limit their use. A conclusion of interest is that where information is at hand on the starting materials (OPC, FA, sand, admixtures), their proportions in the mortar and the mixing liquid content (water or alkaline activators) their radiological content is accurately predicted. The inference is that a mortar’s radiological content and ACI can be known prior to mixing, providing a criterion for determining its viability. That in turn lowers environmental risks and the health hazards for people in contact with such materials.

Revisiting and reanalysing the concept of bioreceptivity 25 years on

2020 marks 25 years since Olivier Guillitte defined the term 'bioreceptivity', to describe the ability of a building material to be colonised by living organisms. Although Guillitte noted in his 1995 paper that several issues required further investigation, to the best of our knowledge the bioreceptivity concept has not been restated, reviewed, reanalysed or updated since then. The present paper provides an opinionated exposition of the status and utility of the bioreceptivity concept for built heritage science and conservation in the light of current knowledge, aimed to stimulate further discussion. A bibliometric analysis highlights the key dimensions of the past 25 years of published research, showing that the term bioreceptivity has been widely used in the field of built cultural heritage. In our reanalysis of the concept, special attention is devoted to the six types of bioreceptivity (primary, secondary, tertiary, intrinsic, extrinsic and semi-extrinsic) articulated by Guillitte in 1995. We propose that field-based studies of bioreceptivity are urgently needed, and that the intrinsic, extrinsic and semi-extrinsic types of bioreceptivity should be dropped, and a new category (quaternary bioreceptivity) added. Additionally, we propose that bioreceptivity in submerged and subsoil environments should also be considered. Bioreceptivity remains an important concept for managing both new build and built heritage, as it provides the key to understanding the drivers and patterns of biological colonisation of building materials.

Cracks in consolidants containing TiO2 as a habitat for biological colonization: A case of quaternary bioreceptivity

The recently proposed concept of quaternary bioreceptivity applies to substrates treated with coating materials and it is considered in the present study with the alga Bracteacoccus minor and the cyanobacterium Nostoc sp. onto granite specimens treated with ethyl silicate and nano-sized silica doped with different amounts of TiO₂ (0, 0.5, 1 and 3 wt%). The findings showed a lack of correlation between the amount of TiO₂ and the level of colonization (main bioreceptivity estimator) to the presence of cracks on the surface, which annul the biocidal power of TiO₂. Crack formation, which depends on the mechanical properties, greatly influences the bioreceptivity of the material. Thus, the cracks provided anchor points where water is retained, in turn strongly influencing the early stages of colonization kinetics, to a greater extent than the biocidal power of TiO₂, which will probably increase as the biofilm develops over the entire surface. In addition, although the cracks were more abundant and wider in the ethyl silicate-based consolidant, the nano-sized silica provided better anchoring points, making the material treated with the corresponding consolidant more bioreceptive.

Impact of colour on the bioreceptivity of granite to the green alga Apatococcus lobatus: Laboratory and field testing

Recent work has demonstrated that surface colour affects the formation of cyanobacterial subaerial biofilms on polycarbonate coupons and, in turn, influences their bioreceptivity. To explore whether colour is important on other substrates, the influence of colour on the primary bioreceptivity of granite to the terrestrial green alga Apatococcus lobatus (Trebouxiophyceae, Chlorophyta) has been assessed. Two granitoids (Grissal and Rosa Porriño) with the same texture, and very similar chemical composition, open porosity and surface roughness, but different coloration related to feldspars (i.e. greyish and reddish) were used to conduct bioreceptivity studies in parallel field and laboratory tests. Light microscopy, colour spectrophotometry, PAM fluorometry, and optical profilometry were used to evaluate colonisation and its impacts. Short-term results (after 7 and 10 weeks of colonisation by a mono-species biofilm) from both lab and field trials, showed significantly more algae growth on reddish granite (Rosa Porriño) than on greyish granite (Grissal). Also, optical profilometry and light microscopy demonstrated that on both granites algal aggregates developed in hollows. We attribute the roughly double levels of A. lobatus growth on reddish vs greyish granite to differences in the amount of radiant energy absorbed and the higher levels of red wavelength light (known to encourage algal growth) reflected from the reddish surface.

A review of the nature, role and control of lithobionts on stone cultural heritage: weighing-up and managing biodeterioration and bioprotection

Lithobionts (rock-dwelling organisms) have been recognized as agents of aesthetic and physico-chemical deterioration of stonework. In consequence, their removal from cultural heritage stone surfaces (CHSS) is widely considered a necessary step in conservation interventions. On the other hand, lithobiontic communities, including microbial biofilms ('biological patinas'), can help integrate CHSS with their environmental setting and enhance biodiversity. Moreover, in some cases bioprotective effects have been reported and even interpreted as potential biotechnological solutions for conservation. This paper reviews the plethora of traditional and innovative methodologies to characterize lithobionts on CHSS in terms of biodiversity, interaction with the stone substrate and impacts on durability. In order to develop the best management and conservation strategies for CHSS, such diagnosis should be acquired on a case-by-case basis, as generalized approaches are unlikely to be suitable for all lithobionts, lithologies, environmental and cultural contexts or types of stonework. Strategies to control biodeteriogenic lithobionts on CHSS should similarly be based on experimental evaluation of their efficacy, including long-term monitoring of the effects on bioreceptivity, and of their environmental safety. This review examines what is known about the efficacy of control methods based on traditional-commercial biocides, as well as those based on innovative application of substances of plant and microbial origin, and physical techniques. A framework for providing a balanced scientific assessment of the role of lithobionts on CHSS and integrating this knowledge into management and conservation decision-making is presented.

Testing Anti-Biofilm Polymeric Surfaces: Where to Start?

Present day awareness of biofilm colonization on polymeric surfaces has prompted the scientific community to develop an ever-increasing number of new materials with anti-biofilm features. However, compared to the large amount of work put into discovering potent biofilm inhibitors, only a small number of papers deal with their validation, a critical step in the translation of research into practical applications. This is due to the lack of standardized testing methods and/or of well-controlled in vivo studies that show biofilm prevention on polymeric surfaces; furthermore, there has been little correlation with the reduced incidence of material deterioration. Here an overview of the most common methods for studying biofilms and for testing the anti-biofilm properties of new surfaces is provided.

Biofilm colonization of metamorphic lithotypes of a renaissance cathedral exposed to urban atmosphere

Stone architectural heritage exposed outdoor represents a challenging habitat for biological growths; nevertheless, biocolonization on heritage structure is ubiquitous and represents a major mechanism of alteration. However, the identification of specific microorganisms with known reactivity towards the stone substrate does not necessarily imply that a biodeterioration process is in progress and, in specific conditions, bioprotection effects have been highlighted as a result of colonization. The main objective of the present research is to evaluate the biofilm formation on different lithotypes exposed to similar environmental polluted conditions, and to investigate whether the presence of subaerial biofilms can be associated to an increased magnitude of deterioration of the colonized surfaces with respect to the not colonized ones. In particular, the research examines the extensive biological colonization of the stone surfaces of the façade of the Cathedral of Monza (Italy). Four metamorphic stones widely used in the façade and showing rather different compositional, mineralogical and microstructural features were studied. The state of conservation of the stones was characterized under the mineralogical and compositional point of view by X-ray diffraction and Fourier Transformed infrared analysis. The microstructure of colonized substrates and of reference not colonized ones was studied by means of optical and electron microscopy, to comparatively evaluate the damage extent and weathering patterns in both conservative conditions. The structure and the architecture of biofilms growing on different lithic surfaces were investigated by CLSM in both fluorescence and reflection modes. Captured images were analyzed for 3D reconstructions of biofilm samples. The biovolumes were also calculated to estimate the total biomass. The results indicate that the four lithotypes showed different colonization extents. However, even in presence of extensive biological growth, chemical-physical deterioration mechanisms caused by environmental exposure were largely responsible for deterioration. A relationship between compositional and surface morphological features and biocolonization was also observed.