Bacterial and fungal communities in the sandstone biofilms of two famous Buddhist grottoes in China

Abstract Microorganisms can accelerate the deterioration of stone monuments. In this study, we used next-generation sequencing (Illumina MiSeq PE300 Platform) to investigate the microbial biofilm communities that have developed on sandstone in two famous Buddhist cave temples, the Maijishan Grottoes and Tiantishan Grottoes, located on the historical Silk Road in western China. We found high bacterial diversity and relatively low eukaryota diversity based on 16S and 18S ribosomal RNA (rRNA) sequencing analysis. The dominant bacterial groups were Cyanobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, and Chloroflexi. The dominant eukaryota were Ascomycota, Basidiomycota, and Chytridiomycota. The most dominant genes among the bacteria were from Cyanobacteria (unclassified and no rank), Pseudonocardia, Kribbella, and Rubrobacter; the dominant fungal genes were from unclassified Lecanorales and Capnodiales (unclassified and norank). These microbes form biofilms that will contribute to biodeterioration of the underlying sandstone. Combining with field monitoring and microscopic analysis, we determined that high bioreceptivity of the sandstone and locally available water were two important exogenous and endogenous factors that promoted microbial colonization, proliferation, and subsequent biofilm formation. The aforementioned microbes usually coexisted on the sandstone surfaces by building an inter-connected and dynamic community capable of adapting to and resisting the harsh local environmental conditions to survive and undergo succession.