Proteomic evaluation of the biodegradation of wool fabrics in experimental burials

Woollen textiles recovered from archaeological excavations are usually fragile, discoloured, mineralised, or highly biodeteriorated fragmentary remains. The nature and extent of preservation is highly dependent on the site of burial and factors such as soil composition, pH, temperature, oxygen content, and contact with a wood coffin or metals. Understanding the particular biodegradation in archaeological sites is important for biomolecular studies of textiles, and to assist in the conservation of these finds. Wool fabrics dyed and buried for up to 8 yr in bog-type soils in Denmark (Lejre) and Norway (Rørmyra), and in marine sediments in Sweden (Marstrand) were evaluated by proteomics analysis. Wool degradation was found to occur through a range of differing mechanisms, mainly due to the complex nature of wool itself with its many families of proteins (keratin and keratin-associated proteins) and structures. Microbial activity was a large contributory factor to the physical deterioration of the wool fabrics at Lejre and Marstrand, and might result in faster loss of keratin-associated proteins over keratins. Additional hydrolysis took place at Marstrand, influenced by the environmental conditions of the sediment, and in particular the alkaline pH, contributing to the degradation of keratins. However, cross-linking was associated with the long-term preservation of the fabrics at Rørmyra, where pH, temperature, and vegetative composition of the bog prevented microbial activity, and sphagnum moss might preserve wool by binding with keratins.