Abstract
Two novel species of the fungal genus Ochroconis, O. lascauxensis and O. anomala have been isolated from the walls of the Lascaux Cave, France. The interest in these fungi and their melanins lies in the formation of black stains on the walls and rock art which threatens the integrity of the paintings. Here we report solid-state cross polarization magic-angle spinning 13C and 15N nuclear magnetic resonance (NMR) spectroscopy and surface-enhanced Raman spectroscopy (SERS) of the melanins extracted from the mycelia of O. lascauxensis and O. anomala in order to known their chemical structure. The melanins from these two species were compared with those from other fungi. The melanins from the Ochroconis species have similar SERS and 13C and 15N NMR spectra. Their chemical structures as suggested by the data are not related to 3,4-dihydroxyphenylalanine, 5,6-dihydroxyindole or 1,8-dihydroxynaphthalene precursors and likely the building blocks from the melanins have to be based on other phenols that react with the N-terminal amino acid of proteins. The analytical pyrolysis of the acid hydrolysed melanin from O. lascauxensis supports this assumption.
Highlights
The microbiology of subterranean environments has received increasing attention due to the biodeterioration processes affecting the integrity of rock art and mural paintings[1,2]
The fungus Ochroconis lascauxensis contributes to the formation of black stains on the walls of the Lascaux Cave[1,8,9,18]
Our results indicate that the presence of aromatic N heterocyclic compounds in Ochroconis melanins is neglectable, if any
Summary
The microbiology of subterranean environments has received increasing attention due to the biodeterioration processes affecting the integrity of rock art and mural paintings[1,2]. Fungi have originated several outbreaks in Lascaux Cave, France[8,9], and colonised Japanese tombs[10]. In this context, the identification of microorganisms involved in the biodeterioration of World Heritage Sites and the knowledge of the chemistry of their secondary metabolic products and melanins is of utmost interest for adopting conservation strategies. The detailed chemical structure of the fungal melanins is not known and microscopic studies showed that melanin granules are localised in the cell wall where they are likely cross-linked to polysaccharides components especially those containing mannose[11]. It becomes evident that the extracted melanins contain cell wall polysaccharides, chitin, proteins and lipids, which makes it difficult to analyse “pure” melanin. Polymerization of the precursors leads to melanin formation[14,15]
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