Seasonal variation of airborne bacteria of the Tiantishan Grottoes and Western Xia Museum, Wuwei

Abstract:

[Background] Microbial deterioration is a common biological disease in ancient wall paintings, which seriously threaten the long-term safety preservation and exhibition of the wall paintings. As the main source of the harmful microorganisms to wall paintings, airborne microorganisms have attracted extensive attention in the monitoring and preventive conservation of cultural relics in recent years. [Objective] systematic survey of culturable airborne bacteria, including the concentration, community structure and seasonal variation, was carried out in environments of wall paintings preserved at Tiantishan Grottoes and Western Xia Museum, China. [Methods] Bio-aerosol sampler containing R2A agar was used for sampling in all four seasons in 2016. Traditional culture-based method to acquire the airborne bacterial concentration information and purified strains; by the extraction of genomic DNA, amplification of bacteria 16S rRNA gene region, sequencing, and phylogenetic analysis, thereafter the bacteria community composition and distribution characteristics of different study sites were clarified. Combined with environmental monitoring data, to disclosure the main factors which responsible for the dynamic changes of the airborne bacteria at the site. [Results] The concentration of culturable airborne bacteria was in a range from 16.7 to 1 451.8 CFU/m3. There was no significant difference in bacteria concentration between the Cave 18 and Cave 13, namely, the two sites at the Tiantishan Grottoes, with the obvious characteristics of the seasonal variation, briefly speaking, Winter and Spring were higher than Summer and Autumn. Meanwhile, there was significant difference in bacteria concentration between the inside and outside of the Xixia Museum, the square outside of the museum were far more than the inside of the museum at the four seasons, particularly in the winter. A total of 19 bacteria genera that affiliated to four phylum were detected, among which, Acinetobacter, Arthrobacter, Bacillus, Kocuria, Brevundimonas, Carnobacterium, Pseudoclavibacter and Hymenobacter were the dominant ones. [Conclusion] The airborne bacterial community structures of the Tiantishan Grottoes showed a distinct characteristic of the seasonal variation and spatial distribution; RH, temperature and seasonal rainfall were all have influences on the airborne bacteria distribution; some of the genera have potential of causing biodeterioration of the ancient wall paintings at this site; this study could provide supporting information for the preventive protection of cultural relics that preserved at local site and museums.

Key words:Airborne bacteria, Community characteristics, Ancient wall paintings, Monitoring and precaution