Bioreceptivity of building stones: a review.

Since ancient time, magnificence and beauty have been the goals of architecture. Artists and architects used high strength, durable and beautiful stones like marble and limestone for the construction of monuments like Taj Mahal, Milan Cathedral, Roman Catacombs and Necropolis in Rome etc. These historic monuments are exposed to open air which allows the invading army of algae, cyanobacteria, fungi etc. to easily access them. The invasion of microorganisms and their subsequent interaction with mineral matrix of the stone substrate under varied environment conditions fosters deterioration of stones by multiple mechanisms resulting in loss of strength, durability, and aesthetic appearance. The review details about the major routes and mechanisms which led to biodeterioration, discusses current remedial methodologies and suggests future directions.

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Microbially induced deterioration of architectural heritages: routes and mechanisms involved

Three coccoid and two filamentous cyanobacterial strains were isolated from phototrophic biofilms exposed to intense solar radiation on lithic surfaces of the Parasurameswar Temple and Khandagiri caves, located in Orissa State, India. Based on to their morphological features, the three coccoid strains were assigned to the genera Gloeocapsosis and Gloeocapsa, while the two filamentous strains were assigned to the genera Leptolyngbya and Plectonema. Eleven to 12 neutral and acidic sugars were detected in the slime secreted by the five strains. The secretions showed a high affinity for bivalent metal cations, suggesting their ability to actively contribute to weakening the mineral substrata. The secretion of protective pigments in the polysaccharide layers, namely mycosporine amino acid-like substances (MAAs) and scytonemins, under exposure to UV radiation showed how the acclimation response contributes to the persistence of cyanobacteria on exposed lithoid surfaces in tropical areas.

Characteristics and role of the exocellular polysaccharides produced by five cyanobacteria isolated from phototrophic biofilms growing on stone monuments.

Biofilm-forming cyanobacteria are widespread inhabitants of exposed stones in archaeological and historical sites and caves. Outdoors, these phototrophic biofilms are adapted to all types of stress imposed by growth at the air-rock interface and have developed the capacity to tolerate excess solar radiation, extreme temperatures and desiccation at different latitudes. Indoors, the typology of the cave or the characteristics of confined environments strongly selects the microbial community according to light availability and air humidity. Interactions of cyanobacteria with rocky substrata serving as the source of mineral nutrients are based on the adhesion mechanisms and metabolic processes that allow the development of these biofilms. Both types of subaerial phototrophic community include cyanobacteria that support associated populations of heterotrophic populations of mostly very specialized species. The distribution of particular cyanobacterial taxa on monuments in urban or agricultural areas is related mostly to climatic conditions and the position and orientation of the hard surface with respect to water availability and air circulation.

Cyanobacterial Biofilms in Monuments and Caves

Biological colonization patterns on the ruins of Angkor temples (Cambodia) in the biodeterioration vs bioprotection debate

Surfaces of buildings at the archaeological site of Palenque, Mexico, are colonized by cyanobacteria that form biofilms, which in turn cause aesthetic and structural damage. The structural characterization and species composition of biofilms from the walls of one of these buildings, El Palacio, are reported. The distribution of photosynthetic microorganisms in the biofilms, their relationship with the colonized substratum, and the three-dimensional structure of the biofilms were studied by image analysis. The differences between local seasonal microenvironments at the Palenque site, the bioreceptivity of stone and the relationship between biofilms and their substrata are described. The implications for the development and permanence of species capable of withstanding temporal heterogeneity in and on El Palacio, mainly due to alternating wet and dry seasons, are discussed. Knowledge on how different biofilms contribute to biodegradation or bioprotection of the substratum can be used to develop maintenance ...

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M. Hernández-Mariné

Papers

Cyanobacteria-containing biofilms from a Mayan monument in Palenque, Mexico