Black mold on a white limestone: the role of Stachybotrys chartarum in stone heritage deterioration

Abstract Fungal deterioration of historical stone objects can significantly impact their mineralogy and chemistry, leading to irreplaceable cultural heritage losses. Ançã stone, a unique type of limestone widely used in some of the most emblematic Portuguese monuments, due to its soft, porous calcium carbonate nature, is known to have a high intrinsic bioreceptivity, being highly susceptible to fungal colonization and subsequent biodeterioration. In a prior experimental study aimed at characterizing the fungal diversity thriving on a Ançã stone funerary art piece showing visible signs of alteration at the Lemos Pantheon, a national monument in Águeda, Portugal, several isolates of an unexpected black mold were obtained. The detection of Stachybotrys chartarum across the multiple approaches used during that investigation suggested that its occurrence was not solely due to environmental contamination, prompting us to conduct a comprehensive analysis, as this species had never been previously associated with this lithotype. Our results proved the presence of S. chartarum , representing the first confirmed occurrence of this species from Ançã stone. Using a multi-locus phylogeny combined with morphological, physiological, and ecological analyses, we characterized these isolates. We also demonstrated the biodeteriorative potential of S. chartarum through plate assays, along with its in vitro ability to actively colonize limestone, with and without organic matter deposition, and solely under the natural fluctuations in relative humidity, causing changes to the substrate. We were able to observe hyphae penetration into calcite layers of inoculated stone probes, potential mineral desegregation and displacement, as well as putative mineralization phenomena around its hyphae after 10 months. This study provides critical new insights into the biodeteriorative potential of S. chartarum , which, along with its well-known toxigenic attributes, adds to its infamous reputation.