Community structures of bacterial colonies on wall paintings in Cave 98 at Mogao Grottoes, Dunhuang

Abstract:

[Objective] In this study, we aimed to observe the detailed features of microbes within white spots adhered to the surface of ancient wall paintings in Cave 98, Mogao Grottoes; meanwhile, we explore microbial community composition and structure characteristics, analyze factors that induce the explosion of microbial diseases on murals; thereafter, our results could serve with scientific support for cave conservation and tourism management. [Methods] Samples of white spots on murals were carefully collected by sterile scalpel and sealed in eppendorf tubes. A part of samples was used for observation of microbes by the scan electronic microscope (SEM); another part was used for the total genomic DNA extraction, followed steps were the bacterial 16S rDNA amplification, clone library construction, sequencing, and phylogenetic analysis, afterwards, the microbial community composition and structure characteristics were clarified. [Results] A number of objects that similar to microbes were observed in white spots of wall paintings, which shaped short rod or ovoid, with the volume ranged among 3.0 μm?5.5 μm multiply by 1.5 μm?2.5 μm. About 111 appropriate sequences were retrieved from clone library in this study. All sequences were similar to members of Enterobacteriaceae and Pseudomonadaceae that both belong to phylum of γ-proteobacteria. Results of community analysis indicated that sequences were mainly affiliated to genus Enterobacter, Escherichia, Azotobacter, Serratia, and Klebsiella; Enterobacter (46.8%) and Escherichia (35.1%) were dominant in our study, both of them are ubiquitous microbes in nature, and human pathogenic bacteria as known. [Conclusion] The white spots on murals in Cave 98 were caused by colony formation of bacterial growth. Members of proteobacteria dominated in the clone library of our study sites. As a result, we speculated that explosion and spread of microbes in Cave 98 was related to long-term tourism in this cave previously.

Key words:Dunhuang murals, Microbial colonies, 16S rDNA, Clone library, Community composition, Structure characteristics, Tourism opening