A novel extremophile strategy studied by Raman spectroscopy

Area of Science:

• * Bio-deterioration and extremophile behavior of lichens on cultural heritage materials.
• * Application of advanced spectroscopic techniques in art conservation.

Background:

• * Ancient wall paintings are susceptible to biodeterioration by microbial colonization.
• * Lichens, particularly Dirina massiliensis forma sorediata, can colonize and degrade these sensitive substrates.
• * Understanding the survival strategies of these organisms is crucial for conservation.

Purpose of the Study:

• * To classify the colonization of pigments on ancient wall paintings by Dirina massiliensis forma sorediata as extremophilic behavior.
• * To identify the survival strategies of this lichen in the presence of heavy metal toxins.
• * To investigate the biodeteriorative effects of lichen encrustations on wall paintings.

Main Methods:

• * Fourier Transform Raman (FT-Raman) spectroscopy was employed to analyze lichen encrustations.
• * Molecular information was extracted to understand the lichen's survival mechanisms.
• * Analysis included identifying biomolecular signatures and mineral components within the lichen thalli and substrate.

Main Results:

• * FT-Raman spectroscopy identified the production of a carotenoid, likely astaxanthin, on the lichen thalli surface.
• * Calcium oxalate dihydrate (weddellite) was detected on both surfaces and within the rock substrate up to 10mm deep.
• * Unexpectedly, no evidence of oxalic acid complexation with metal pigments was found, contrary to previous studies.

Conclusions:

• * The lichen's survival strategy involves producing carotenoids for protection and calcium oxalate for substrate degradation.
• * The presence of weddellite explains the significant biodeteriorative impact on wall paintings, informing conservation efforts.
• * The absence of metal-ligand complexation suggests unique metabolic interactions or environmental conditions in this specific case.