Structure of melanins from the fungi Ochroconis lascauxensis and Ochroconis anomala contaminating rock art in the Lascaux Cave

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.

Characterization of melanin and optimal conditions for pigment production by an endophytic fungus, Spissiomyces endophytica SDBR-CMU319

“…endophytica was soluble in alkali solutions, insoluble in water and organic solvents and salt solutions, precipitated in HCl solution, decolorized in the presence of oxidizing agents and displayed positive reactions for polyphenols by producing flocculent brown precipitation with FeCl 3 . These characteristics were also exhibited in the synthetic melanin and are common to various microbial melanin’s as have been described in previous studies [25, 27, 29, 35, 45, 47].…”

“…Notably, some fungal melanin were present in the fungal structures (e.g. cell wall, appressoria and spore) or secreted into the cultivated medium [16, 24–26, 28, 27, 45, 46]. However, the present study has provided the first report on melanin pigments being produced by S .…”

“…Extraction and purification of pigment from a dried fungal biomass was performed as a described method by De la Rosa et al [27] and Rajagopal et al [29] with some modifications. Fungal pigment derived from 1 g of dried fungal biomass was dissolved in 5 ml of 1 mol/L KOH, allowed to stand for 48 h and autoclaved (20 min at 121°C).…”

Yellow coloured mats from lava tubes of La Palma (Canary Islands, Spain) are dominated by metabolically active Actinobacteria

“…The identification of 3,5-dimethoxy-4-hydroxy-cinnamaldehyde by analytical pyrolysis, a yellow phenolic compound, in the pyrolysate of the yellow microbial mat evidences this assertion and it is hypothesized that lignin phenols could also contribute to the colour observed on the lava tubes walls. In general, most of the compounds identified by analytical pyrolysis are common thermal evaporation/degradation products of lipids, carbohydrate and proteins either in microorganisms or plants 27 , 55 . The cinnamaldehyde and β-sitosterol derivatives point to a direct plant origin 27 , 56 .…”

Fungal stains on paper: is what you see what you get?

“…On sample D3-E, on the other hand, an isolate from S. chartarum was identified, which could result from crosscontamination, since D3-A and D3-E were closely located. S. chartarum, a known paper colonizer [39][40], is a melanin producer [41], hence the black colour of its colony. Being a producer of highly toxic mycotoxins [42], the identification of such a developed colony of S. chartarum on this document alerts to potential health hazards related to the handling of fungal contaminated objects.…”