Microbiome and response to cleaning and biocidal treatments on granite historical buildings using MinION sequencing

Abstract

On built cultural heritage, research into cleaning and biocides impact on microbiome (preferably bacteria) is gaining increased interest. Communities’ changes induced by the chemical treatments and underlying aspects related to the microorganisms within biofilms susceptibility and resistance to antimicrobial treatments are still understudied. This research, through a field survey in two granite-built eighteenth-century monuments in Santiago de Compostela (NW Spain), aimed to determine how two sources of chemicals: (1) from an intervention (restoration treatment with ammonium bicarbonate and biocides based on quaternary ammonium salts - Biotin R® and New Des® 50 -) carried out 15 years ago on the building facade, and (2) from street cleaning (made with water containing aliphatic amines, quaternary compounds and potassium hydroxide), currently carried out every two days and only reaches the building facade indirectly due to the dispersion of aerosols, have affected the microbiome. Samples from greening and no-greening areas were taken from both buildings. Microbial community composition and functional profiles, including resistance genes, were assessed using Oxford Nanopore whole-metagenome sequencing. The study findings reveal that the impact of street cleaning on the bacterial microbiome was greater than that of restoration treatment, with neither chemicals’ application causing a pattern in the fungal microbiome composition. Both bacterial and fungal diversity were higher in the sampling areas affected by street cleaning, whereas antibiotic resistance genes (ARGs) and biocide resistance genes (BRGs) appeared more frequently in areas that underwent restoration treatment 15 years ago.