Mogao Grottoes, a UNESCO World Cultural Heritage Site since 1987, suffer from microbial colonization and deterioration of the wall paintings with visible appearance of black spots and fungal colonization in selective caves. In this study, Next-Generation Sequencing (NGS) and microscopical analyses were combined and used to reveal the microbial community compositions on wall paintings of the Mogao Grottoes. In addition, radioactive 14 C dating was applied to determine the possible infestation time of the fungal outbreak in history based on Bayesian chronological modeling. Results of SEM, fluorescence microscopy and polarizing microscopy showed collectively that the existing microbial hyphae were not viable. The dominant bacteria included Rhodococcus and Ralstonia mainly with unclassified_c_Eurotiomycetes while Aspergillus species were the predominant mycoflora in samples of the black spots and microbial biomass. Using 14 C dating results and historical documents together, the original mural was most likely painted in the Five Dynasties and Ten Kingdoms (939-942 ca. AD) while the repainting time and the mural were mostly probable in Song Dynasty (1002-1014 ca. AD), and the fungal remains were most likely formed in this historical period. With monitoring locations closer to the cliff, the higher bacterial diversity and lower fungal diversity detected were correlated with the higher relative humidity. Since the temperature and relative humidity were generally low in this area, unsuitable for microbial growth presently or in the normal time of the past, either earthen plaster preparation prior to the first painting or heavy rainfall events and leaky roof was most likely the initiator to the outbreak of the indigenous microbes to proliferate on the wall paintings. This study provided useful evidences on the microbial community and the time of a microbial outbreak event on ancient wall paintings in such an extremely arid climate condition.
- Wall paintings
- Microbial deterioration
- 14C dating
- Rainfall and relative humidity
- Cultural heritage conservation