Microbial induced stone discoloration in alcobaça monastery: A comprehensive study

Abstract

The Alcobaça Monastery (Portugal), a UNESCO World Heritage Site, currently exhibits a high degree of surface alterations of the stone architectural elements inside the church, including an extensive pink coloration in the walls and columns, bacteria biofilms, and salt efflorescences. The main goal was to identify the microbiota that colonizes the walls and columns of this monument, to help custodians and conservators-restorers in the selection of the correct procedure to be adopted for the conservation of the monument. Regarding the observed pink discoloration, and considering previous studies, we hypothesize that is caused by biofilms formed by bacteria or other microorganisms that produce pigments of the same color, particularly carotenoids. Curiously, a distinct phenomenon was noticed: the pink discoloration always seems to appear at a very similar height in most of the columns and walls, starting at 40 cm to the floor and associated with the presence of salts on the walls. Using high-throughput sequencing approaches, we were able to characterize the microbial community present. We identified several bacteria that are producers of pink pigments and halotolerant such as Rubrobacter radiotolerans, Domibacillus robiginosus, Bacillus licheniformis and Halalkalicoccus sp. that develop in areas of high salinity.