Biodeterioration of cultural heritage monuments: a review of their deterioration mechanisms and conservation

Geochemical cycles result in the chemical, physical, and mineralogical modification of rocks, ultimately leading to the formation of soil. However, when stones and rocks form part of historic buildings and monuments, the effects are deleterious. In addition, microorganisms colonize these monuments over time, resulting in the formation of biofilms, while microbial metabolites cause physical weakening and discoloration of the stone. This process, known as biodeterioration, results in a significant loss of cultural heritage. Purification and 16S rDNA sequencing of bacteria growing on heritage monuments revealed that the most prominent taxa were closely related to Bacillus spp., Arthrobacter spp., Staphylococcus spp. and Paenibacillus spp. In addition to bacteria, some fungal strains of the genera Penicillium, Aspergillus, Fusarium and Alternaria were also reported. To formulate effective conservation strategies to prevent biodeterioration and restore monuments, it is important to identify the microorganisms colonizing the substrate and the energy sources they utilize for sustenance. With this perspective, this review focuses on studies that explored the process of biodeterioration, the mechanisms by which microbes colonize and impact monuments, the techniques used to assess biodeterioration and conservation strategies designed to preserve the monuments.