Cyanobacteria in biofilms on stone temples of Bhubaneswar, Eastern India

The exterior facades of several stone temples of Bhubaneswar (eastern India), built during the 6th to 13th centuries, are now covered with blackish-brown biofilms dominated by cyanobacteria. The architectural carvings show various degrees of deterioration of lithic faces underneath the biofilms, indicating the contribution of these phototrophic microorganisms to this process. A total of 17 species of cyanobacteria, belonging to the genera Gloeocapsa, Gloeocapsopsis, Porphyrosiphon, Leptolyngbya, Lyngbya, Phormidium, Nostoc, Scytonema, Tolypothrix, Hassallia and Stigonema were found in biofilms during the hot months of the tropical summers. The organisms were identified on the basis of their morphological features and those species that were isolated in pure culture were taxonomically validated by 16S rRNA gene sequencing. The temperature at the exterior of these stone monuments exceeds 60°C, especially during summer, coupled with extreme dryness. Consequently, only cyanobacteria are able to form biofilms. In contrast, during the rainy season, biofilms contained 25 additional cyanobacteria species belonging to the genera Cyanosarcina, Gloeocapsopsis, Phormidium, Pseudophormidium, Schizothrix, Lyngbya, Plectonema, Nostoc, Scytonema, Tolypothrix, Dichothrix and Calothrix together with the green alga Chlorella sphaerica.