Mechanism of dyeing technique of Xiang-yun-sha and bioaugmentation of its coating mud with iron reducing bacteria

Abstract

The dyeing technique of Xiang-yun-sha , with a history of more than 600 years, is a kind of unique hand-made dyeing process that combines both plant dyeing (immersed with Juliang extract) and mineral dyeing (mud coating). It has been included in the national intangible cultural heritage. However, the scientific mechanism of this heritage has not been systematically explained. In this study, the composition and structure of Juliang were analyzed with ionizing-spray high-resolution mass spectrometry and infrared spectroscopy, and the interaction mechanism of the Juliang with silk protein was explored. The mud-coating process was explained from the molecular level through a chemical simulation method, and the maintenance effect of microbes on characteristics of river mud was examined. Results showed that there are phenol and quinone of catechin condensed tannin in the Juliang extract, and they were combined with silk protein peptide bonds through multi-sites hydrogen bonds. The gial pigments on the silk surface after exposure further reacted with Fe(II) in the mud to form soluble condensed tannin complex, and then this complex was rapidly oxidized to form black precipitate containing Fe(III). Eventually, lustrous dark brown was formed on sun side, brown on the other side. Further, it was found that microbial iron reduction played a key role on maintaining the mud properties, because the addition of Shewanella decolorationis S12 with iron reducing function can significantly improve the dyeing performance of unqualified mud. This study provides reliable scientific support to protect inheritance of dyeing technique and promote the standardized production of the industry.