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BIOCOLONIZATION AND BIODETERIORATION OF MONUMENTS BY CYANOBACTERIA

Cyanobacteria are a morphologically diverse, remarkably adaptable and widely distributed group of photosynthetic prokaryotes, many of which colonize, grow and survive on/in water-limited and nutrient-poor lithic substrates, such as natural rocks/stones and walls of historic monuments and buildings as lithobionts or lithobiontic organisms. They are often the primary colonizers of lithic substrates. They possess protective mechanisms against various abiotic stresses, such as desiccation, high irradiance, high levels of UV-radiation and high temperature which are often encountered on exposed rock surfaces and external walls of lithic monuments and buildings. The biocolonization and growth of cyanobacteria as lithobionts are influenced by various propertiesof monuments, buildings or buildingstones as well as by environmental factors. As photoautotrophs and primary colonizers of lithic substrates, they facilitate and promote the growth and development of heterotrophic microbes, such as bacteria and fungi.The production of extracellular polymeric substances (EPS) leads to the formation of cyanobacteriadominated phototrophic biofilms or sub-aerial biofilms on exposed surfaces of monuments, buildings and rocks/stones. Globally, thebiocolonization, growth and activities of lithobiontic cyanobacteria and other organisms cause unpleasant discoloration, biodeterioration (bioweathering) of monuments and buildings of historical, cultural or religious importance, leading to the aesthetic damage, structural damage and economic loss.These constitute serious problems world-wide. The article provides an overview of the processes of biocolonization and biodeterioration of monuments by lithobiontic(rockinhabiting) cyanobacteria, and their survival as lithobionts.