Mycogenic minerals formation by airborne Aspergilli and Penicillia
Formation of secondary mycogenic minerals, a phenomenon often reported on artworks, is heavily associated with both structural and aesthetic alterations of affected masterpieces. The aim of this study was to investigate capabilities of airborne Aspergillus and Penicillium species, common contaminants of works of art, to induce mineral formation in vitro. For this purpose, tested fungal isolates were cultivated on B4 medium, and optical microscopy and SEM-EDS techniques were applied to observe the morphology of crystals and to discern their chemical composition. Out of 34 isolates in total, mineral formation was documented in 14 Aspergilli and 15 Penicillia species. The predominant crystal in the investigated samples was calcium oxalate, while calcium carbonate crystals were only seldom reported. Biogenesis of secondary mycogenic minerals is probably due to the ability of investigated isolates to excrete different acidic metabolites into the substrata. Investigations of biomineralization of autochthonous airborne fungal isolates must not be neglected for adequate protection of stone-made cultural heritage objects. However, little focus is given to this phenomenon, especially concerning formation of oxalates via fungal metabolites.