Analysis of salt-containing biofilms on limestone buildings of the Mayan culture at Edzna, Mexico

Biofilms on the salted ceiling of a limestone tunnel at the Mayan site of Edzna, Mexico, were characterised using SEM, EDS, chemical analysis, light microscopy, culture and pigment analysis. Major superficial biomass was pigmented, scytonemin-rich Subsection II cyanobacteria. Main endolithic phototrophs were Subsection I and II cyanobacteria and the alga Nanochlorum. Bacteria and actinomycetes of the Geodermatophilus, nocardioform, and streptomycete groups were present at all levels. Salt crystals, mainly sulfates, were found throughout the stone. Microbial ion transport, metabolite production, chelation, and water retention caused degradation and salt deposits. Exfoliation is the major erosion process.