Back to the past—forever young: cutting-edge biochemical and microbiological tools for cultural heritage conservation

The role of essential oils as eco-friendly strategy to control biofilm collected in the Colosseum (Rome, Italy)

The control of biodeteriogenic microorganisms is essential for the management of heritage sites. Many conventional biocides are no longer available because they have lost their efficacy or have been withdrawn from the market due to their danger to humans and the environment. Therefore, new effective and sustainable biocides are needed, such as plant extracts that could be a good alternative. In this study, essential oils (EOs) of Ocimum basilicum L., Cinnamomum verum Presl, Lavandula angustifolia Mill., Origanum vulgare L., Thymus vulgaris L. and Melaleuca alternifolia Maiden & Betche were tested as green biocides against microorganisms collected from biofilms in the hypogeum of the Colosseum (Rome, Italy). Biocidal screening was first carried out on phototrophic microorganisms grown on BG11 agar culture medium. The efficacy was assessed by measuring photosynthetic activity with a mini-PAM portable fluorometer, and by determining morphological changes or the absence of autofluorescence using light microscopy and confocal laser scanning microscopy. The most effective EOs against phototrophs were further tested to inhibit the growth of heterotrophic fungi and bacteria in order to identify those with a broad-spectrum action. The EOs of cinnamon, oregano and thyme at 5% concentration (v/v) were the most effective against the microorganisms isolated from the biofilms in the Colosseum. These EOs represent a green alternative to traditional chemical biocides due to their activity against a wide range of microorganisms and their complex composition which suggests the potential to reduce the risk of microbial resistance. KEY POINTS: Biofilms collected from the Colosseum hypogeum were characterized EOs tested as biocides against phototrophs and heterotrophs in Colosseum biofilms. Cinnamon, oregano, and thyme EOs show broad-spectrum action at 5% concentration.

Autofluorescence for the Visualization of Microorganisms in Biodeteriorated Materials in the Context of Cultural Heritage

Microorganisms, including fungi, bacteria, cyanobacteria, and algae, frequently colonize the surfaces of cultural heritage materials. These biological agents can cause biodeterioration through various mechanisms, resulting in aesthetic alteration, physical disruption, or compromise of mechanical integrity. To assess the presence and diversity of microorganisms, a combination of microscopy techniques is commonly used in conjunction with results from both culture-dependent and culture-independent methods. However, microbial populations are often underestimated. To address this issue, microorganisms can be detected by their intrinsic fluorescence, which can be observed via fluorescence microscopy. This approach facilitates the mapping of the spatial arrangement of microorganisms and the understanding of colonization patterns, thereby complementing established imaging techniques and providing insight into the interactions of microbial communities with the substrate. Given the limited research in this area, we examine the potential of microorganism autofluorescence as a molecular tool for investigating biodeterioration in artistic and architectural heritage, with a particular focus on paper and stone materials. Identifying and understanding the diverse microbiota that may be present is crucial for developing tailored and effective preventive measures and conservation treatments, as some of the species discovered may pose significant risks to both artifacts and human health.

Wheat-Based Glues in Conservation and Cultural Heritage: (Dis)solving the Proteome of Flour and Starch Pastes and Their Adhering Properties

Plant-based adhesives, such as those made from wheat, have been prominently used for books and paper-based objects and are also used as conservation adhesives. Starch paste originates from starch granules, whereas flour paste encompasses the entire wheat endosperm proteome, offering strong adhesive properties due to gluten proteins. From a conservation perspective, understanding the precise nature of the adhesive is vital as the longevity, resilience, and reaction to environmental changes can differ substantially between starch- and flour-based pastes. We devised a proteomics method to discern the protein content of these pastes. Protocols involved extracting soluble proteins using 0.5 M NaCl and 30 mM Tris-HCl solutions and then targeting insoluble proteins, such as gliadins and glutenins, with a buffer containing 7 M urea, 2 M thiourea, 4% CHAPS, 40 mM Tris, and 75 mM DTT. Flour paste's proteome is diverse (1942 proteins across 759 groups), contrasting with starch paste's predominant starch-associated protein makeup (218 proteins in 58 groups). Transformation into pastes reduces proteomes' complexity. Testing on historical bookbindings confirmed the use of flour-based glue, which is rich in gluten and serpins. High levels of deamidation were detected, particularly for glutamine residues, which can impact the solubility and stability of the glue over time. The mass spectrometry proteomics data have been deposited to the ProteomeXchange, Consortium (http://proteomecentral.proteomexchange.org) via the MassIVE partner repository with the data set identifier MSV000093372 (ftp://MSV000093372@massive.ucsd.edu).

Removal of overpainting from an historical painting of the XVIII Century: A yeast enzymatic approach

Biocleaning of cultural heritage items is mainly performed using living microorganisms. Approaches utilizing the enzymes of isolated microorganisms have not been frequently investigated. To find an enzymatic alternative for the removal of an oil-based overpainting, we focused on the characterization and use of a yeast Extracellular Enzymatic Mixture (EEM). A historical silk yeast was selected for its lipolytic properties and its EEM was extracted after cultivation on a medium supplemented with linseed oil. The EEM protein content was visualized by SDS-PAGE, its concentration assessed by fluorimeter and the enzymatic activity evaluated by p-NPP spectrophotometric lipase assay. The yeast growth was suppressed by adding diverse metal ions (Cd, Zn, Cr and Cu) in Reasoner's 2A (R2A) broth, while the quantity and activity of EEM were affected by adding Fe and Pb. Various delivery systems (agar-agar, tylose and klucel G) alone or in a combination with EEM were assayed on the historical painting surface. The colorimetric measurements and the ATR-FTIR analysis indicated that the combinations tylose-EEM and klucel G-EEM can be easily and effectively applied as biocleaning procedures to remove oil-based overpainting from fragile and valuable historical painting surfaces.

The Bad and the Good-Microorganisms in Cultural Heritage Environments-An Update on Biodeterioration and Biotreatment Approaches

Cultural heritage objects constitute a very diverse environment, inhabited by various bacteria and fungi. The impact of these microorganisms on the degradation of artworks is undeniable, but at the same time, some of them may be applied for the efficient biotreatment of cultural heritage assets. Interventions with microorganisms have been proven to be useful in restoration of artworks, when classical chemical and mechanical methods fail or produce poor or short-term effects. The path to understanding the impact of microbes on historical objects relies mostly on multidisciplinary approaches, combining novel meta-omic technologies with classical cultivation experiments, and physico-chemical characterization of artworks. In particular, the development of metabolomic- and metatranscriptomic-based analyses associated with metagenomic studies may significantly increase our understanding of the microbial processes occurring on different materials and under various environmental conditions. Moreover, the progress in environmental microbiology and biotechnology may enable more effective application of microorganisms in the biotreatment of historical objects, creating an alternative to highly invasive chemical and mechanical methods.

Immobilized Enzymes on Gold Nanoparticles: From Enhanced Stability to Cleaning of Heritage Textiles

Enzyme-based treatments are used in heritage conservation for the effective removal of glues and other damaging organic layers from the surfaces of historic and artistic works. Despite their potential, however, the application of enzymatic treatments is currently limited because of their poor efficiency and low operational and environmental stability. We demonstrate the use of α-amylase immobilized on gold nanoparticles to improve the efficacy of enzymatic treatments enhancing both the reactivity and the stability of the formulations. Gold nanoparticles coated with α-amylase exhibit significant advantages compared to free enzymes. We report up to 5× greater resistance to environmental changes, up to 2× higher efficacy toward removal of starch-based glues from textiles and deeper penetration through the fibers, without causing damage or inducing salt precipitation. These results offer exciting prospects for the development of enzymatic formulations, both for heritage conservation and the wider application of enzymes, such as in medicine, the detergent industry, and green chemistry.