Three different phototrophic microbial communities colonizing a single natural shelter containing prehistoric paintings

Three different cases of deterioration were identified in a single natural shelter containing prehistoric paintings. The microbial communities induced by run-off water, a black crust covering a portion of the shelter, and a cryptoendolithic microbial community, were studied. Molecular analyses based both on DNA and RNA were performed to identify the major components of these microbial communities present and metabolically active, respectively, at the studied location. While similar microbial communities were expected due to the proximity of the studied sites, clearly different communities were detected suggesting that specific microorganisms adapt to different micro-environments. Phototrophic microorganisms represented the major portion of total RNA and DNA in the studied microbial communities. Run-off water induced the presence of a large proportion of putative photosynthetic bacteria belonging to Chloroflexi. Different groups of bacteria were associated to phototrophs and were represented by Alpha, Beta, Delta, and Gammaproteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, and Planctomycetes. The present study confirms a need for careful monitoring of microbial communities associated to distinct cases of deterioration even within a single location, underlining the interest of phototrophic microorganisms as indicators of colonization on cultural heritage at natural shelters.