Characterisation of brown-rot decay in the historic Lejonström bridge using X-ray tomography and molecular identification of associated fungi

The deterioration of wooden heritage structures requires regular monitoring, particularly when pressure-impregnated Scots pine is exposed to moisture and biological degradation. This study assessed fungal degradation of structural elements of the Lejonström bridge in Skellefteå, Sweden’s oldest wooden bridge and a culturally significant monument. Non-destructive X-ray tomography identified internal decay based on reduced density, brown-rot characteristics, and microbial colonisation. Culturable fungi were isolated from decayed wood and identified by ITS-based Sanger sequencing. In total, 37 pure cultures representing 17 fungal species from 11 genera were obtained. Most isolates were saprotrophic, mould, or wood-associated ascomycetes typical of weathered or decayed wood. Two basidiomycetes, Amyloporia xantha and Crustoderma sp., were associated with areas showing brown-rot symptoms, suggesting their contribution to timber degradation. A. xantha was the most frequently isolated basidiomycete. These findings improve understanding of fungal communities involved in biodegradation and support monitoring and preservation strategies for wooden heritage structures in Sweden.