Biogenesis of secondary mycogenic minerals related to wall paintings deterioration process

Abstract

Present study addresses potential of fungal strains, isolated from deteriorated mural paintings and surrounding air environment of the Church of the Holy Ascension in Veliki Krčimir (Serbia), to precipitate mycogenic minerals, when cultivated on agarized B4 medium. Utilizing culture-based isolation methods, 38 filamentous fungi were obtained in total, 23 from mural paintings and 15 from air, respectively, mainly ascomycetes, while Bjerkandera adusta and Thanatephorus cucumeris were only basidiomycetes. A total of 31 of 38 fungal isolates, more than 80%, were able to form minerals of different morphologies and variable size, determined via SEM-EDS and XRPD, to be either calcite or calcite and weddellite association. Among screened fungi, all Penicillium, Chaetomium and Cladosporium isolates, as well as most of the Aspergillus isolates (8/11) precipitated minerals, whereas cultures of Bionectria, Bjerkandera, and Seimatosporium isolates lacked any observable crystal forms. With the exception of two Alternaria alternata strains, no apparent disparity in potential to precipitate minerals in general, or form particular crystal phase was documented among the air and mural paintings isolates. Possible mechanisms of fungal mineralization of calcite and weddellite are further proposed. In addition to providing experimental evidence for fungal induced precipitation of oxalate and carbonate minerals, presented data suggest that fungal activity could be an important factor in a weathering process affecting cultural heritage exhibited and stored in inadequate conditions. Implementation of B4 plate assay for screening of mineralization potential of the isolated fungi could be used to assess biodegradative risk mycobiota pose to the mural paintings, so appropriate conservation measures may be utilized.