Thermal environment driving specific microbial species to form the visible biofilms on the UNESCO World Heritage Dazu Rock Carvings

Abstract

The Dazu Rock Carvings, a UNESCO World Heritage site with over a millennium of history, are facing significant deterioration from microbial biofilms. However, the key microbial species responsible and the environmental factors driving their growth remain unclear. To address this gap, we conducted metagenomic sequencing to characterize the microbial community on the carvings, followed by correlation analyses with a variety of environmental factors in the surrounding air and within the rocks. Bacterial communities exhibited significantly higher richness and diversity than eukaryotic communities, though diversity metrics showed no significant differences between visibly colonized and uncolonized surfaces. We identified a distinctive consortium of 64 bacterial species, 35 fungal species, and 1 algal species specifically associated with visible biofilms, occurring at 9.56-fold higher relative abundance in colonized areas. These microorganisms contribute to characteristic green, brown-black, and white coloration on the carvings. Statistical analysis revealed absolute humidity and dew point temperature as key environmental factors influencing biofilm visibility, with thresholds of 21.00 g/m³ and 23.4 °C respectively, above which biofilms became visible. This study provides precise targets for conservation efforts and establishes critical environmental parameters to guide preservation strategies for this irreplaceable cultural heritage.