Colonization and survival of a stress tolerant cyanobacterium on a heritage monument of Santiniketan, India

Colonization of cyanobacteria and associated algae on a heritage monument (Buddha statue) of Santiniketan, India was studied. The dominating biofilms component is a filamentous cyanobacterium, Scytonema millei, which thrives on the monument, even when the surface temperature exceeds 60 °C during summer. The basic adaptive strategy of S. millei was analysed upon exposure to different temperature range and desiccation based on the changes in growth, morphology, and biochemical analysis. Maximum increase of growth (16.2%), chlorophyll-a (42.2%), carotenoids (24.4%), cellular carbohydrate content (102.2%), extracellular carbohydrate content (643.6%), and SOD activity (134.8%) were observed under stress conditions. The organism was found as desiccation and thermo-adaptive species. S. millei was more tolerant to heat soon after exposure in the dry state than in the wet state. Significant increase in carbohydrate content (cellular and extracellular) and SOD activity upon exposure to stress suggests their main importance in the stress tolerance of S. millei. These findings suggest that the dominating cyanobacteria have developed different defense mechanisms enough to survive in extreme natural conditions of tropical regions as well as in lab conditions. •Spatial distribution of cyanobacteria and algae on a heritage monument was studied.•Cyanobacteria and green algae colonized on exposed and shady parts respectively.•Scytonema millei was found as a desiccation and thermo-adaptive cyanobacterium.•Survival strategy of Scytonema millei was investigated.•Carbohydrate and SOD activity seems crucial for stress tolerance.