Controlling Lampenflora in Heritage Sites: In Situ Testing of Polyoxometalate–Ionic Liquids in the Pommery Champagne Cellar

Artificial lighting, essential for geotouristic purposes in subterranean sites, has facilitated the growth of colored photosynthetic organisms (lampenflora) on monumental 19th century bas-reliefs of the Pommery Champagne cellar-a UNESCO-protected heritage site-causing significant aesthetic and physical deterioration. To sustainably preserve these stone artworks, biocidal polyoxometalate-ionic liquids (POM-ILs) are tested alongside the commercial biocide Preventol RI80 on three trial zones: cleaned and colonized areas of a wall and clean stone samples positioned on a testing station within the cellar. After 1 year, untreated control areas exhibit growth/regrowth of biofilms, whereas surfaces treated with POM-ILs or Preventol RI80 remain biofilm free. Measurements of colorimetry and chlorophyll fluorescence confirm the effectiveness of both biocides in controlling photosynthetic micro-organisms. However, confocal fluorescence microscopy highlights a reduced long-term inhibition by Preventol RI80 compared to POM-ILs, despite the latter being applied at lower concentrations. Metagenomic analysis further validates the performance of POM-ILs, showing a notable decrease in microbial richness and diversity in treated areas. While both products effectively inhibit phototrophs and fungi, their efficacy against Pseudomonadota is limited, likely due to microbial adaptation via antibiotic resistance genes. This study underscores the potential of POM-ILs as a sustainable alternative for preserving cultural heritage against microbial colonization.