Characterization of bacterial community inhabiting the surfaces of weathered bricks of Nanjing Ming city walls

Nanjing Ming city wall, one of the important historic heritages in China, has greatly suffered weathering. Microbes play an important role in the weathering of historic buildings. However, little is known about the microbial community inhabiting naturally weathered brick minerals and their roles in the mineral weathering. To examine the associations between microorganisms and brick weathering process, we compare the phylogenetic diversity, abundance, community structure, and specific functional groups of bacteria existing in weathered bricks by using a coupled approach involving cultivation-independent analysis of denaturing gradient gel electrophoresis (DGGE) as well as cultivation-based analysis of Si-releasing bacteria. DGGE and sequence analyses show that the bacterial communities were different along a weathering gradient and the abundance of bacterial communities positively and significantly correlates with the extent of brick weathering. Laboratory brick mineral dissolution experiments indicate that bacteria isolated from the surfaces of weathered brick were very effective in enhancing brick dissolution. Phylogenetic analyses show that the weathered bricks were inhabited by specific functional groups of bacteria (Bacillus, Massillia, Brevibacillus, Glacialice, Acinetobacter, Brachysporum, and Achromobacter) that contribute to the brick weathering.

Research highlights
► DGGE analyses indicated that the highly-weathered bricks inhabited higher bacterial diversity than the lowly-weathered bricks.
► The abundance of bacterial communities correlates with the extent of brick weathering.
► Bacteria isolated from the surfaces of the weathered bricks were very effective in enhancing brick dissolution.
► Phylogenetic analyses show that the weathered bricks were inhabited by specific functional groups of bacteria that contribute to the brick weathering.