Mycobiota of silk-faced ancient Mogao Grottoes manuscripts belonging to the Stein collection in the British library

Silking, a conservation technique which involved gluing silk gauze over the face of a manuscript was popular in the mid-20th Century, especially for treating early Chinese documents. The method is now little used, and the question as to whether silking interventions should be reversed is controversial, given the high economic cost of active intervention, and there are few scientific studies as to the long-term consequences of the technique. Silk-facing materials from documents of the Stein collection were analysed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The mycobiota diversity was unravelled through the combination of culture dependent methods and amplicon sequencing analyses. The SEM micrographs showed smooth regular nodules of ca. 3–5 μm diameter on both silk threads and glue paste. This morphology differs from the irregular and the crystalline morphologies of glue paste and inorganic crystallites, respectively, but it is consistent with that of small-sized conidia (asexual spores of fungi) or yeasts. Glue paste demonstrated three fungal strains: Aspergillus tubingensis, Penicillium crustosum and Chrysonilia sitophila which display cellulolytic activity, except for the last one. Amplicon sequencing revealed that silk threads and glue paste host distinct mycobiota. Here, we preliminary show that the silking method may be affecting the overall integrity of the silk-faced manuscripts, principally due to contamination with cellulolytic fungal strains. Unless the silk facing is removed, irreversible damage to the documents is highly probable.