Microbial Deterioration of Heritage Monuments in Santiniketan, West Bengal, India

Microbial deterioration of monuments and facades of heritage buildings is a well-known and a widely recognized problem in India and the world over. Several stone monuments of archaeological importance, belonging to period from the 1st to 12th century AD in many regions of India have become obliterated, defaced and disfigured due to the colonization of blackish/brownish growth of biofilms on their exposed surfaces, causing aesthetic/structural disfigurement and damage^1,2. The main species of these biofilms thriving on Indian monuments are cyanobacteria, which are stress-tolerant and can survive in the adverse condition of desiccation and extreme temperature of stones^3–5. During the onset of monsoon, these blackish/brownish biofilms become greenish after absorbing moisture and utilize the minerals present in the stone substrata to grow. This is the main cause of deterioration of these important monuments^6–8. Certain species of cyanobacteria which dominate these biofilms, develop survival strategies by secreting a thick sheath of extracellular polymeric substances (EPS) resulting into crust formation under adverse conditions and desiccation^9,10. These cyanobacteria are also rich in UV-sunscreen pigments like scytonemin and mycosporine- like amino acids (MAAs)¹¹ which act as a protective mechanism against desiccation and intense solar radiation^12,13.