The Stain of the Original Salt: Red Heats on Chrome Tanned Leathers and Purple Spots on Ancient Parchments Are Two Sides of the Same Ecological Coin

Nicoletta Perini; Fulvio Mercuri; Maria Cristina Thaller; Silvia Orlanducci; Domenico Castiello; Valerio Talarico; Luciana Migliore

doi:10.3389/fmicb.2019.02459

The Stain of the Original Salt: Red Heats on Chrome Tanned Leathers and Purple Spots on Ancient Parchments Are Two Sides of the Same Ecological Coin

Front Microbiol. 2019 Oct 29:10:2459. doi: 10.3389/fmicb.2019.02459. eCollection 2019.

Authors

Nicoletta Perini¹, Fulvio Mercuri², Maria Cristina Thaller¹, Silvia Orlanducci³, Domenico Castiello⁴, Valerio Talarico⁴, Luciana Migliore¹

Affiliations

¹ Department of Biology, Tor Vergata University of Rome, Rome, Italy.
² Department of Industrial Engineering, Tor Vergata University of Rome, Rome, Italy.
³ Department of Chemical Science and Technology, Tor Vergata University of Rome, Rome, Italy.
⁴ Po.Te.Co. s.c.r.l., Santa Croce sull'Arno, Italy.

Abstract

Animal hides are one of man's earliest and mostly used materials; many rawhide products, primarily leather, have for centuries been used for several purposes. The peculiar mechanical properties of leather depend on the hide composition, a dense collagen feltwork. Unfortunately, due to their proteic composition, rawhides may undergo microbial attack and biodeterioration. Over centuries, different processes and treatments (brining, vegetal or chrome tanning, tawing, etc.) were set up to face the biological attack and modify/stabilise the hide's mechanical properties. Nevertheless, even present-day rawhides are subjected to biological colonisation, and traces of this colonisation are clearly shown in Chrome(III) tanned leathers (in the wet blue stage), with obvious economic damages. The colonisation traces on tanned leathers consist of isolated or coalescent red patches, known as red heat deterioration. Parchments are rawhide products, too; they derive from another manufacturing procedure. Even parchments undergo microbial attack; the parchment biodeterioration seems comparable to leather red heat deterioration and is known as purple spots. Recently, an ecological succession model explained the process of historical parchment purple spot deterioration; the haloarchaea Halobacterium salinarum is the pioneer organism triggering this attack. The marine salt used to prevent rawhide rotting is the carrier of haloarchaea colonisers (Migliore et al., 2019). The aim of this study was to investigate the dynamics of biodeterioration on Chrome(III) tanned leathers and its effects on the stability/integrity of collagen structure. To this end, standard cultivation methods were integrated with three updated technologies, Next-Generation Sequencing (NGS), Raman spectroscopy, and Light Transmitted Analysis (LTA). A bioinformatic comparison between chrome tanned leather vs. historical parchment colonisers was performed to evaluate if leather and parchment share common culprits; furthermore, the effect of the biodeterioration on the physical properties of the hide product was evaluated.

Keywords: Halobacterium salinarum; leather; parchment; purple spot deterioration; red heat deterioration; salt-curing of hides; tanned rawhides.