Sulfur-oxidizing bacteria involved in the blackening of basalt sculptures of the Leizhou Stone Dog

Leizhou Stone Dog is the unique stonework in the Leizhou Peninsula, which has a history of more than two thousand years, representing its great significance of art and culture. However, most of these stone dogs are suffering from severe physical, chemical and biological attacks, biodeterioration in particular. In this study, we determined bacterial communities in the biofilms on the stone dogs and explored the potential mechanisms on blackening of the basalt sculptures. Bacterial communities in the biofilms were dominated by Proteobacteria, followed by Cyanobacteria, Chloroflexi, Acidobacteriota, Actinobacteriota, Armatimonadota, Bacteroidota, Deinococcota, Firmicutes, Gemmatimonadota, Planctomycetota, and Verrucomicrobiota. Interestingly, the two genera Sulfurovum and Acidiphilium, which are typical sulfur-oxidizing bacteria, were dominated in the black biofilms. Contents of selective soluble ions, especially for Cl- and SO42?, NO3? were detected higher in soil under the sculptures. Moreover, X-ray fluorescence spectroscopy analysis revealed that Fe and Ca are the major elements in the black biofilms, which are widely reported to be two main elements of black crusts composed of FeS or CaSO4 on stone monuments. Our findings provide potential chemical and microbial evidence for sulfuroxidizing bacteria involved in the blackening of basalt sculptures of the Leizhou Stone Dog.

Automated summary

The Leizhou Stone Dog is a unique stone sculpture with a history of over two thousand years, but is facing severe physical, chemical, and biological deterioration. This study found that bacterial communities in the biofilms on the sculptures were dominated by Proteobacteria, with sulfur-oxidizing bacteria like Sulfurovum and Acidiphilium being prevalent in the black biofilms. Analysis also showed higher levels of Cl-, SO42?, and NO3? ions in the soil under the sculptures, indicating potential chemical evidence for the involvement of sulfuroxidizing bacteria in the blackening of the basalt sculptures.