Abstract
The preservation of cultural heritage is one of the major challenges of today’s society. Parchments, a semi-solid matrix of collagen produced from animal skin, are a significant part of the cultural heritage, being used as writing material since ancient times. Due to their animal origin, parchments easily undergo biodeterioration: the most common biological damage is characterized by isolated or coalescent purple spots, that often lead to the detachment of the superficial layer and the consequent loss of written content. Although many parchments with purple spot biodegradative features were studied, no common causative agent had been identified so far. In a previous study a successional model has been proposed, basing on the multidisciplinary analysis of damaged versus undamaged samples from a moderately damaged document. Although no specific sequences were observed, the results pointed to Halobacterium salinarum as the starting actor of the succession. In this study, to further investigate this topic, three dramatically damaged parchments were analysed; belonging to a collection archived as Faldone Patrizi A 19, and dated back XVI-XVII century A.D. With the same multidisciplinary approach, the Next Generation Sequencing (NGS, Illumina platform) revealed DNA sequences belonging to Halobacterium salinarum; the RAMAN spectroscopy identified the pigment within the purple spots as haloarchaeal bacterioruberin and bacteriorhodopsine, and the LTA technique quantified the extremely damaged collagen structures through the entire parchments, due to the biological attack to the parchment frame structures. These results allowed to propose a model of the progressive degradation pattern of the parchment collagen. Overall, these data validate a multi-phase microbial succession model. This demonstration is pivotal to possible new restoration strategies, important for a huge number of ancient documents.
Highlights
The most used writing support in ancient times was parchment, a semi-solid matrix of collagen produced from animal skin
The purple spot damage of ancient parchments was studied by an interdisciplinary approach, comparing hardly purple vs uncoloured areas from three dramatically damaged parchments archived as Faldone Patrizi A 19 in the Vatican Secret Archives, dated back to XVI-XVII century A.D
I-XVIII 3328, studied by the same interdisciplinary approach[1], the Raman analysis detected the trace of the past presence of Haloarchaea, even in the absence of any amplifiable DNA
Summary
The most used writing support in ancient times was parchment, a semi-solid matrix of collagen produced from animal skin (i.e. sheep or goats). The Light Transmission Analysis technique bared the collagen structural damage in the purple areas: bacteria cause the thinning out of the interfibers collagen texture and some deterioration of the fibre sheath, the more chemically stable kind of collagen. Basing on these results, a biodeterioration model was hypothesized and proposed. These documents were chosen due to the deep and widespread purple spot damage, leading even to the loss of significant portion of the documents In these extremely damaged conditions, we supposed that the pioneer species could have been more largely present at the beginning of the document history, so that they would have been more likely identified. The documents were analysed by the same multidisciplinary approach used in the previous study: NGS metagenomic analysis (Illumina platform), Raman spectroscopy and LTA analysis
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