The microbial community characteristics of ancient painted sculptures in Maijishan Grottoes, China

Abstract

In this study, a culture-independent Illumina MiSeq sequencing strategy was applied to investigate the microbial communities colonizing the ancient painted sculptures of the Maijishan Grottoes, a famous World Cultural Heritage site listed by UNESCO in China. Four mixed samples were collected from Cave 4-4 of the Maijishan Grottoes, the so-called Upper Seven Buddha Pavilion, which was built during the Northern Zhou Dynasty (557-581AD). The 16/18S rRNA gene-based sequences revealed a rich bacterial diversity and a relatively low fungal abundance, including the bacterial groups Actinobacteria, Acidobacteria, Bacteroidetes, Cyanobacteria, Chloroflexi, Firmicutes, Proteobacteria and Verrucomicrobia and the fungal groups Ascomycota, Basidiomycota and Chytridiomycota. Among them, the bacteria genera of Pseudonocardia and Rubrobacter and unclassified fungi in the order of Capnodiales were dominant. The relative abundance of Pseudonocardia in the painted layer samples was higher than that in the dust sample, while Cyanobacteria dominated in the dust sample. Many of them have been discovered at other cultural heritage sites and associated with the biodeterioration of cultural relics. The presence and activity of these pioneering microorganisms may lead to an unexpected deterioration of the painted sculptures that are preserved in this heritage site. Thus, proper management strategies and potential risk monitoring should be used in the Maijishan Grottoes to improve the conservation of these precious painted sculptures.

Fig 1. The research site and the sampling locations in the grottoes.

A: The geographical location of the Maijishan Grottoes in China; B: Cave 4–4 of the Maijishan Grottoes; C, D and E: the painted statues inside Cave 4–4 and the sampling locations, samples a-c were collected from the Shakyamuni sculpture on the east side, were mixed thoroughly and were named it as MJ4-1. Similarly, samples d-f and g-I were collected from the Bodhisattva sculpture on the south and north sides, respectively. They were also pooled together and were named MJ4-2 and MJ4-3, respectively. Samples 1, 2 and 3 were mixed and were named MJ4-4.

Fig 2

Relative abundance of the bacterial community at the phylum (A) and genus (B) level.

Fig 3. Relative abundance of the fungal community at the family level.

Fig 4. Heat map representation and cluster analysis of the microbial community among four samples.

Bacterial (A) and fungal (B) distributions of the top 50 abundant genera and families, respectively. The double hierarchical dendrogram shows the bacterial and fungal distribution. The bacterial and fungal phylogenetic trees were calculated using the neighbor-joining method.

Fig 5. Principal components analysis.

Scatter plot of the PCA-score showing the similarity of the bacterial (A) and fungal (B) communities based on the Unifrac distance.

Fig 6. Shared OTU analysis of the different samples.

Venn diagram showing the unique and shared OTUs (97%) for the bacterial (A) and fungal (B) communities among the four samples.