Molecular identification and GC-MS analysis of cyanobacteria and algae isolated from historic monuments in Uttarakhand

Biodeterioration of stone monuments is primarily caused by microorganisms such as cyanobacteria and green algae, which act as pioneer organisms colonizing stone surfaces. The biodeterioration of these monuments poses a significant threat to cultural heritage, particularly in environments with large fluctuations in temperature and humidity. The present study, conducted during 2022–2023, involved sample collection from four historical stone monuments in Uttarakhand, i.e., Tungnath Mahadev Temple (Rudraprayag District), Beatles Ashram (Dehradun District), Koteshwar Mahadev Temple (Rudraprayag District), and Tapkeshwar Mahadev Temple (Dehradun District). Cyanobacteria and green algae were identified as the principal stone-surface colonizers, forming biofilms that promote decay. These microorganisms occur in epilithic, chasmolithic, and endolithic forms, producing exopolysaccharides (EPS) that enhance surface adhesion, retain moisture, and protect against UV radiation. The EPS matrix further facilitates the establishment of new microbial communities, thereby accelerating the degradation of the stone substrate. GC–MS analysis was employed to identify the major compounds present in five selected isolates. The analysis revealed several prominent peaks, among which 9-octadecenoic acid methyl ester, methyl n-hexadecanoate, isoborneol, phytol, and hexadecanoic acid methyl ester were the dominant components, representing a significant proportion of the total chemical composition. These metabolites are associated with microbial adherence, biofilm formation, and stone deterioration. Notably, isoborneol and phytol have been reported to interfere with bacterial attachment and quorum sensing, influencing biofilm regulation and stability. This study establishes green algae and cyanobacteria as key biodeteriogens contributing to biological growth and stone dissolution through EPS secretion and metabolic activity. Their colonization of the aforementioned Uttarakhand monuments underscores the urgent need for sustainable, eco-friendly conservation strategies to protect and preserve these invaluable cultural heritage sites.