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Differences of Microbial Community on the wall paintings preserved in situ and ex situ of the Tiantishan Grottoes, China

Duan, Yulong, Wu, Fasi, Wang, Wanfu, Gu, Ji-Dong, Li, Yanfei, Feng, Huyuan, Chen, Tuo, Liu, Guangxiu, An, Lizhe
International biodeterioration & biodegradation 2018 v.132 pp. 102-113
Acidobacteria, Bacteroidetes, Basidiomycota, Cyanobacteria, Deinococcus-Thermus, Firmicutes, Fusobacteria, Promicromonospora, Proteobacteria, Sordariales, Trichocomaceae, biodegradation, caves, cultural heritage, ex situ conservation, fungi, gypsum, microbial communities, ribosomal RNA, China
Tiantishan Grottoes, a famous site well known for its historical status in the spread of Buddhism art in ancient China, were selected for a comparison and analysis of microbial taxonomic characteristics on the wall paintings under different preservation conditions: in situ and ex situ conservation. A total of 12 samples were collected from three different cave wall paintings preserved in situ or ex situ. The 16/18S rRNA gene-based sequences revealed a high bacterial diversity and a relative low fungal abundance, including bacterial groups Firmicutes, Actinobacteria, Proteobacteria, Bacteroidetes, Cyanobacteria, Acidobacteria, Deinococcus-Thermus and Fusobacteria; and fungal groups Ascomycota and Basidiomycota. Among them, two bacterial genera of the Promicromonospora and Planomicrobium and fungal order of the Sordariales and the family of Trichocomaceae were dominant in the samples preserved ex situ. Some of them have been reported at other cultural heritage sites and associated with the biodeterioration of cultural relics. The over-growth of these microbes led to the abundant filaments formed visible on the surface of the ex situ wall paintings, which preserved under museum conditions. Application of preservation materials including animal glue and wet gypsum to take them off from grottoes and strengthen, and subsequent long-term preservation under poor conditions in museums were mainly responsible for the microbial outbreaks. To avoid similar problems in the future, reasonable intervention measures and strict micro-environmental control must be implemented to the ex situ preservation of wall paintings. Our results have profound significance for clarify the occurrence of microbial invasions and mechanisms on the wall paintings; it is helpful to development a reasonable artificial intervention measures for conservation work of the wall paintings in the future.