Identification of Bacterial Communities Involved in Bioweathering Crusts on Limestone Sculptures of the Longmen Grottoes

Abstract

Bioweathering crusts are widely distributed on the limestone sculptures of the Longmen Grottoes, a UNESCO World Heritage Site. However, information on microbial communities in this archaeological site is missing. To fill this gap, we identified bacterial communities involved in the formation of bioweathering crusts. The composition analysis showed that Cyanobacteria, Acidobacteria, Chloroflexi, Actinobacteria, Firmicutes, and Planctomycetota are the major components of the bacterial communities in the crusts. Cyanobacteria might be one of the major contributors to the formation of the crusts. A culture-based analysis indicated the presence of bacterial isolates (e.g., Enterobacter sp. and Bacillus sp.) with a potential role in bioprotection. Moreover, five types of biogenic organic acids were detected in the crusts, implying a consequence of organic acid corrosion. Scanning electron microscopy analysis further confirmed microbial penetration into the stone monuments with a biomechanical attack. Our reports provide a microbiological reference for heritage conservators to treat bioweathering crust.