Fungi and Stone Heritage Conservation: Friend, Foe, or a Bit of Both.

The presence of lithobionts has historically been associated with biodeterioration, posing significant challenges to the conservation of culturally and historically significant stone heritage. This perception stems from abundant evidence of their role in biogeophysical processes, such as mechanical disruption of stone structures, and biogeochemical processes, which chemically alter stone composition through metabolic activity. These processes, while integral to natural systems, often accelerate the weathering and deterioration of heritage materials. Coupled with the aesthetic impact of lithobiont growth, frequently resulting in discoloration or obscuring of intricate details, such effects have justified the widespread removal of these organisms from heritage surfaces. However, recent research has revealed a far more nuanced picture. These communities can enhance biodiversity, contribute to the perceived authenticity of aged monuments, and, in some cases, form a biological layer that shields stone from pollutants and weathering forces. Moreover, developments in biomediated conservation approaches, such as biocementation and biocleaning, highlight their potential as sustainable allies in preservation. This dual role of lithobionts-both as friends and foes in preservation-is central to this review. This review focuses on how these organisms-with a particular emphasis on fungi, often perceived as enemies of conservation-may also serve as unexpected partners in safeguarding our stone heritage, emphasizing the need for case-by-case evaluation of active communities and their environmental context.