Difference and environmental drivers of bacterial communities on wall paintings of the Maijishan and Mogao Grottoes, China

Wenxia Ma^1*Qiqi Chen¹Fasi Wu²Dongpeng He²Yulong Duan³Yongqiang Yue²Ji-Dong Gu⁴Xiaoyan Yang¹Huyuan Feng¹

• ¹Lanzhou University, Lanzhou, China
• ²Dunhuang Research Academy, Dunhuang, China
• ³Northwest Institute of Eco-Environment and Resources, Lanzhou, China
• ⁴Guangdong Technion-Israel Institute of Technology, Shantou, China

The Maijishan Grottoes and Mogao Grottoes, both UNESCO World Heritage Sites along the Silk Road, are increasingly threatened by microbial biodeterioration. This study aimed to characterize bacterial communities colonizing wall paintings in these grottoes and identify the environmental factors shaping their composition. High-throughput DNA/RNA sequencing was combined with microenvironmental monitoring to assess microbial diversity and activity, followed by a systematic comparison between the two sites. At Maijishan, bacterial communities associated with black and white mycelia showed no significant compositional differences within the same cave but varied markedly between caves, indicating site-specific community assembly. Actinobacteria (>50%), particularly Pseudonocardia and Actinomycetospora, predominated, while RNA-based analysis revealed active populations of Escherichia and Stenotrophomonas, likely introduced via exogenous contamination from animal activities. In contrast, black spots from the Mogao Grottoes were dominated by Actinobacteria, Firmicutes, and Proteobacteria, with Rhodococcus as a core genus. No core bacterial OTUs were shared between the sites, suggesting strong microenvironmental filtering. Multivariate analysis identified substrate properties (total organic carbon, total nitrogen, pH) and microclimatic fluctuations (diurnal temperature/humidity ranges) as critical drivers. Maijishan's persistently humid conditions (RH >70% for over 180 days/year) favored Actinobacteria proliferation, whereas Mogao's arid climate (RH <70% for over 240 days/year) selected for xerotolerant Firmicutes. These results reveal distinct site-specific microbial colonization patterns and provide a scientific basis for targeted conservation strategies to mitigate microbial damage and preserve these invaluable wall paintings.