Diversity and biodeteriorative potential of fungal dwellers on ancient stone stela

Abstract

Biodeterioration caused by fungal colonizers on an ancient stone stela, excavated from the former Roman settlement (Eastern Serbia) was investigated. According to selected biodeterioration elements, average deterioration index was assessed (0.8), prompting the need for conservation. Fungal somatic and reproductive structures, along with lichen thalli and moss fragments, were detected on the surface using different microscopy and cultivation methods. In situ microscopy on the site was implemented, for the first time, in the study of stone monuments. Biodeteriorative potential of 5 selected isolates was tested using qualitative biochemical tests, SEM-EDS and XRPD analyses. Fusarium proliferatum and Penicillium crustosum altered the pH value in broth minimal medium. Pigment production was demonstrated for F. proliferatum, while P. crustosum showed potential for calcite dissolution. All isolates induced biomineralization on solid medium with calcium acetate, where weddellite, calcite and subordinate whewellite crystals were confirmed via SEM-EDS and XRPD. Weddellite and calcite production was documented for P. crustosum in solid medium with calcium carbonate. Conservation treatment was carried out with benzalkonium chloride-based biocide, in addition to mechanical treatment. After conservation, in situ microscopy showed deteriorated stone surface covered with residual lichen thalli fragments, while mycelium and reproductive structures of micromycetes were not detected.