A sub-aerial biofilms investigation and new approach in biocide application in cultural heritage conservation: Holy Virgin Church (Gradac Monastery, Serbia)

Abstract

Sub-aerial biofilms (SAB) on frescoes and façade of the Holy Virgin Church (Gradac Monastery, Serbia) were investigated to study the effectiveness of benzalkonium chloride (BAC) as a biocide. Antifungal activity of Origanum vulgare essential oil as a natural product with confirmed high fungicidal potential was also tested against fungi causing alterations on the frescoes. Chemical and mineralogical composition of the church historical mortar showed the dominance of calcareous minerals. In large areas on the church façade, coloured biopatinas formed by different groups of coccoid and filamentous cyanobacteria, green algae and filamentous fungi were found. Epilithic lichens and bryophytes were also present on the church exterior suggesting long-term ecological succession. The presence on the frescoes, of human pathogenic fungus Aspergillus fumigatus were found in the internal environment. Aspergillus and Penicillium species isolated from painted walls were subject to an in vitro biocidal assay with the biocide BAC. An aqueous solution of 0.25% and 0.15% BAC was able to reduce the viability of all the tested fungal isolates after exposure to the solution for 5 min, while exposure to an aqueous solution of 0.05% for 30 min reduced conidial viability. Origanum vulgare essential oil also showed strong antifungal potential against selected fungal isolates.