Controlling Lampenflora in Heritage Sites: In Situ Testing of POM-ILs in the Pommery Champagne Cellar.

Artificial lighting, essential for geotouristic purposes in subterranean sites, has facilitated the growth of colored photosynthetic organisms (lampenflora) on two 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) were 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 one year, untreated control areas exhibited growth/regrowth of green biofilms, whereas surfaces treated with POM-ILs or Preventol RI80® remained biofilm-free. Measurements of colorimetry and chlorophyll fluorescence confirmed the effectiveness of both biocides in controlling photosynthetic microorganisms. However, confocal fluorescence microscopy highlighted a reduced long-term inhibition by Preventol RI80® compared to POM-ILs, despite the latter being applied at lower concentrations. Metagenomic analysis validated the performance of POM-ILs, showing a notable decrease in microbial richness and diversity in treated areas. While both products effectively inhibited phototrophs and fungi, their efficacy against Pseudomonadota was limited, 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.