Rock-dwelling cyanobacteria: survival strategies and biodeterioration of monuments

Cyanobacteria (Blue-green algae) are a morphologically diverse and widely distributed group of photosynthetic prokaryotes endowed with remarkable adaptability to varying environmental conditions and effective protective mechanisms against various abiotic stresses (e.g., desiccation, high light intensity, solar UV radiation and oxidative stress) which enable them to colonize and inhabit almost all kinds of terrestrial and aquatic habitats, including extreme lithic habitats, such as rocks and walls of monuments and buildings. The rock-dwelling (lithobiontic) cyanobacteria grow both as epiliths and endoliths. As a major and dominant component of biofilms or crusts on exposed surfaces, they are responsible for the biodeterioration and aesthetically unacceptable discoloration of buildings and monuments of historical, cultural or religious importance. The biodeterioration of monuments caused by cyanobacteria and other microbes constitute a major problem of world-wide concern, posing a challenge to their conservation and restoration.