Scripta manent? Assessing microbial risk to paper heritage

Long-term monitoring of the hypogeal Etruscan Tomba degli Scudi, Tarquinia, Italy. Early detection of black spots, investigation of fungal community, and evaluation of their biodeterioration potential

AIMS

Hypogeal environments with cultural heritage interest pose a real challenge for their preservation and conservation. The ancient Etruscan Necropolis of Tarquinia, Italy, consists of 200 tombs decorated with extraordinary mural paintings, of great artistic and historical value. Since the beginning of the restoration campaign in 2016, a regular microbiological survey has been performed in the Tomba degli Scudi. The aim of this study was to investigate the nature of an expansion of black spots on the pictorial layers recently observed.

METHODS AND RESULTS

To determine the origin of the black spots in the atrium chamber of the Tomba degli Scudi, the fungal community was sampled using various techniques: cellulose discs, swabs, and nylon membranes and investigated by a multi-analytical approach. The obtained results suggest that the identified fungal strains (e.g. Gliomastix murorum and Pseudogymnoascus pannorum) are common to many subterranean environments around the world, such as Lascaux cave.

CONCLUSIONS

The continuous and long-term monitoring made it possible to detect alterations at an early stage and assess the harmfulness of different fungal strains. This work is a demonstration of the effectiveness of prevention and monitoring actions within these fragile and valuable environments.

Metabarcode insights into the airborne fungal diversity in the indoor and outdoor environments in archives from Yunnan, Southwestern China

Monitoring dynamics of airborne fungal species and controlling of harmful ones are of vital importance to conservation of cultural relics. However, the evaluation of air quality and the community structure characteristics of microorganisms, especially fungi, in the atmosphere of archives is in a stage of continuous exploration though more than 4,000 archives were constructed in China. Seventy-two air samples were collected in this study under different spatial and weather conditions from the archives of Kunming Medical University, located in the Kunming metropolitan area, Yunnan province, southwestern China. A total of 22 airborne fungal classes, 160 genera and 699 ASVs were identified, the species diversity is on the rise with the strengthening of air circulation with the outside space, and thus the intensive energy metabolism and activity were found in the spaces with window and sunny weather, except for the higher lipid synthesis of indoor samples than that of outdoor ones. Furthermore, there were significant differences in fungal community composition and abundance between sunny and rainy weathers. A considerable number of species have been identified as indicator in various environmental and weather conditions of the archives, and temperature and humidity were thought to have significant correlations with the abundance of these species. Meanwhile, Cladosporium and Alternaria were the dominant genera here, which may pose a threat to the health of archive professionals. Therefore, monitoring and controlling the growth of these fungal species is crucial for both conservation of paper records and health of archive professionals.

Fungal and bacterial species richness in biodeteriorated seventeenth century Venetian manuscripts

Historical paper documents are susceptible to complex degradation processes, including biodeterioration, which can progressively compromise their aesthetic and structural integrity. This study analyses seventeenth century handwritten historical letters stored at the Correr Museum Library in Venice, Italy, exhibiting pronounced signs of biodeterioration. The techniques used encompassed traditional colony isolation on agar plates and proteomics analyses, employing nanoscale liquid chromatography coupled with high-resolution mass spectrometry (nano-LC-MS). Fluorescence microscopy was used for the first time in the historical paper biodeterioration context to supplement the conventional stereoscopic, optical, and scanning electron microscopic imaging techniques. This method enables the visualisation of microorganisms beyond and beneath the paper's surface through their natural intrinsic autofluorescence in a non-invasive and non-destructive way. The results demonstrate a diverse, complex, and abundant microbiota composed of coexisting fungal and bacterial species (Ascomycota, Mucoromycota, Basidiomycota, Proteobacteria, and Actinobacteria), along with mite carcasses, insects, parasites, and possibly protists. Furthermore, this study reveals certain species that were not previously documented in the biodeterioration of historical paper, including human pathogens, such as Histoplasma capsulatum, Brucella, Candida albicans, and species of Aspergillus (A. flavus, A. fumigatus, A. oryzae, A. terreus, A. niger) known to cause infections or produce mycotoxins, posing substantial risk to both artefacts and humans.

Microbes on the "peachy spots" of ancient Kaihua paper: microbial community and functional analysis

Kaihua paper is a type of precious hand-made paper in China that has been used throughout Chinese history. Due to its extraordinary whiteness and fine texture, it was adopted by the imperial palace in the reign of Emperor Kang Xi and Yong Zheng of the Qing Dynasty of China in the 17th and 18th century. It is stained by a special type of yellowish-brown spot after years of storage, which is called a "peachy spot." The formation of such spots remains unclear, although complicated physicochemical processes or microbial activities might be involved. We performed nondestructive sampling and high-throughput sequencing on peachy spot surfaces, unstained areas, and air samples in the stack room to analysis the the bacterial and fungal communities, and performed prediction of functional genes of the bacterial communities. The results showed that peachy spot formation was mainly related to bacterial communities rather than fungal communities. Significantly more potential acid- producing, acidophilic or cellulase-producing bacteria, such as, Streptococcus, Staphylococcus, and Lysinibacillus, and pigment-producing bacteria, such as Methylobacterium and Rubrobacter, were identified in the peachy spot samples. Prediction of the functional genes of the bacterial community also suggested the production of acidic substance pigments. These findings provide new insights into the pigment formation mechanism in ancient paper and open an opportunity to develop new strategies to preserve the ancient paper documents.

Artefact Profiling: Panomics Approaches for Understanding the Materiality of Written Artefacts

This review explains the strategies behind genomics, proteomics, metabolomics, metallomics and isotopolomics approaches and their applicability to written artefacts. The respective sub-chapters give an insight into the analytical procedure and the conclusions drawn from such analyses. A distinction is made between information that can be obtained from the materials used in the respective manuscript and meta-information that cannot be obtained from the manuscript itself, but from residues of organisms such as bacteria or the authors and readers. In addition, various sampling techniques are discussed in particular, which pose a special challenge in manuscripts. The focus is on high-resolution, non-targeted strategies that can be used to extract the maximum amount of information about ancient objects. The combination of the various omics disciplines (panomics) especially offers potential added value in terms of the best possible interpretations of the data received. The information obtained can be used to understand the production of ancient artefacts, to gain impressions of former living conditions, to prove their authenticity, to assess whether there is a toxic hazard in handling the manuscripts, and to be able to determine appropriate measures for their conservation and restoration.

Imaging and micro-invasive analyses of black stains on the passepartout of Codex Atlanticus Folio 843 by Leonardo da Vinci

This paper accounts for the diagnostic campaign aimed at understanding the phenomenon of black stains appeared on the passepartout close to the margins of Folio 843 of Leonardo da Vinci's Codex Atlanticus. Previous studies excluded microbiological deterioration processes. The study is based on a multi-analytical approach, including non-invasive imaging measurements of the folio, micro-imaging and synchrotron spectroscopy investigations of passepartout fragments at different magnifications and spectral ranges. Photoluminescence hyperspectral and lifetime imaging highlighted that black stains are not composed of fluorescent materials. μATR-FTIR imaging of fragments from the passepartout revealed the presence of a mixture of starch and PVAc glues localized only in the stained areas close to the margin of the folio. FE-SEM observations showed that the dark stains are localized inside cavities formed among cellulose fibers, where an accumulation of inorganic roundish particles (∅100-200 nm in diameter size), composed of Hg and S, was detected. Finally, by employing synchrotron μXRF, μXANES and HR-XRD analyses it was possible to identify these particles as metacinnabar (β-HgS). Further research is needed to assess the chemical process leading to the metacinnabar formation in the controlled conservation condition of Leonardo's Codex.

Antifungal Substances Produced by Xenorhabdus bovienii and Its Inhibition Mechanism against Fusarium solani

Fungal colonization can severely damage artifacts. Nematode endosymbiotic bacteria exhibit good prospects in protecting artifacts from fungal damage. We previously found that supernatant from the fermentation of nematode endosymbiotic bacterium, Xenorhabdus bovienii, is effective in inhibiting the growth of Fusarium solani NK-NH1, the major disease fungus in the Nanhai No.1 Shipwreck. Further experiments proved that X. bovienii produces volatile organic compounds (VOCs) that inhibit NK-NH1. Here, using metabolomic analysis, GC–MS, and transcriptomic analysis, we explored the antifungal substances and VOCs produced by X. bovienii and investigated the mechanism underlying its inhibitory effect against NK-NH1. We show that X. bovienii produces several metabolites, mainly lipids and lipid-like molecules, organic acids and derivatives, and organoheterocyclic compounds. The VOCs produced by X. bovienii showed two specific absorption peaks, and based on the library ratio results, these were predicted to be of 2-pentanone, 3-(phenylmethylene) and 1-hexen-3-one, 5-methyl-1-phenyl. The inhibition of F. solani by VOCs resulted in upregulation of genes related to ribosome, ribosome biogenesis, and the oxidative phosphorylation and downregulation of many genes associated with cell cycle, meiosis, DNA replication, and autophagy. These results are significant for understanding the inhibitory mechanisms employed by nematode endosymbiotic bacteria and should serve as reference in the protection of artifacts.

Demonstration of Allium sativum Extract Inhibitory Effect on Biodeteriogenic Microbial Strain Growth, Biofilm Development, and Enzymatic and Organic Acid Production

To the best of our knowledge, this is the first study demonstrating the efficiency of Allium sativum hydro-alcoholic extract (ASE) againstFigure growth, biofilm development, and soluble factor production of more than 200 biodeteriogenic microbial strains isolated from cultural heritage objects and buildings. The plant extract composition and antioxidant activities were determined spectrophotometrically and by HPLC-MS. The bioevaluation consisted of the qualitative (adapted diffusion method) and the quantitative evaluation of the inhibitory effect on planktonic growth (microdilution method), biofilm formation (violet crystal microtiter method), and production of microbial enzymes and organic acids. The garlic extract efficiency was correlated with microbial strain taxonomy and isolation source (the fungal strains isolated from paintings and paper and bacteria from wood, paper, and textiles were the most susceptible). The garlic extract contained thiosulfinate (307.66 ± 0.043 µM/g), flavonoids (64.33 ± 7.69 µg QE/g), and polyphenols (0.95 ± 0.011 mg GAE/g) as major compounds and demonstrated the highest efficiency against the Aspergillus versicolor (MIC 3.12-6.25 mg/mL), A. ochraceus (MIC: 3.12 mg/mL), Penicillium expansum (MIC 6.25-12.5 mg/mL), and A. niger (MIC 3.12-50 mg/mL) strains. The extract inhibited the adherence capacity (IIBG% 95.08-44.62%) and the production of cellulase, organic acids, and esterase. This eco-friendly solution shows promising potential for the conservation and safeguarding of tangible cultural heritage, successfully combating the biodeteriogenic microorganisms without undesirable side effects for the natural ecosystems.

Decoding the biological information contained in two ancient Slavonic parchment codices: an added historical value

This study provides an example in the emerging field of biocodicology showing how metagenomics can help answer relevant questions that may contribute to a better understanding of the history of ancient manuscripts. To this end, two Slavonic codices dating from the 11th century were investigated through shotgun metagenomics. Endogenous DNA enabled to infer the animal origin of the skins used in the manufacture of the two codices, while nucleic sequences recovered from viruses were investigated for the first time in this material, opening up new possibilities in the field of biocodicology. In addition, the microbiomes colonizing the surface of the parchments served to determine their conservation status and their latent risk of deterioration. The saline environment provided by the parchments selected halophilic and halotolerant microorganisms, which are known to be responsible for the biodegradation of parchment. Species of Nocardiopsis, Gracilibacillus and Saccharopolyspora, but also members of the Aspergillaceae family were detected in this study, all possessing enzymatic capabilities for the biodeterioration of this material. Finally, a relative abundance of microorganisms originating from the human skin microbiome were identified, most probably related to the intensive manipulation of the manuscripts throughout the centuries, which should be taken with caution as they can be potential pathogens.

Protecting books from mould damage by decreasing paper bioreceptivity to fungal attack using decoloured cell-free supernatant of Lysobacter enzymogenes C3

AIMS

To evaluate whether decoloured cell-free supernatant of Lysobacter enzymogenes C3 can decrease paper bioreceptivity to fungal attack.

METHODS AND RESULTS

To prepare colourless C3 supernatant, single-factor design and uniform design were applied. The optimum conditions with high decolouration degree and low antifungal activity loss were achieved as follows: carbon granule content 1·6% (M/V), temperature 27°C, decolouring time 1·2 h and pH 8·0. An agar plate bioassay was used to assess the antifungal activity of the decoloured supernatant against the fungal isolates obtained from contaminated books, and strong suppression was observed. Small-sacle laboratory test was further introduced, in which common book papers were artificially inoculated with the fungal isolates, and then sprayed uniformly with decoloured supernatant or water. The results showed that, after treatment, the paper showed a significantly low extent of fungal colonization and high tensile strength, and maintained the same colour before and after treatment.

CONCLUSION

These results suggest that the decoloured C3 supernatant inhibits fungal growth on types of paper commonly used in books.

SIGNIFICANCE AND IMPACT OF THE STUDY

Decoloured C3 supernatant could be used as a preventive agent to protect books and other paper-based items against fungal growth.

Melding the Old with the New: Trends in Methods Used to Identify, Monitor, and Control Microorganisms on Cultural Heritage Materials

Microbial activity has an important impact on the maintenance of cultural heritage materials, owing to the key role of microorganisms in many deterioration processes. In order to minimize such deleterious effects, there is a need to fine-tune methods that detect and characterize microorganisms. Trends in microbiology indicate that this need can be met by incorporating modern techniques. All of the methods considered in this review paper are employed in the identification, surveillance, and control of microorganisms, and they have two points in common: They are currently used in microbial ecology (only literature from 2009 to 2015 is included), and they are often applied in the cultural heritage sector. More than 75 peer-reviewed journal articles addressing three different approaches were considered: molecular, sensory and morphological, and biocontrol methods. The goal of this review is to highlight the usefulness of the traditional as well as the modern methods. The general theme in the literature cited suggests using an integrated approach.

Microbial Community Analyses of the Deteriorated Storeroom Objects in the Tianjin Museum Using Culture-Independent and Culture-Dependent Approaches

In the storeroom C7 of the Tianjin Museum, one wooden desk and two leather luggages dated back to Qing dynasty (1644-1912 AD) presented viable microbial contamination. The aim of the present study was to investigate microbial communities responsible for the biodeterioration of storeroom objects using a combination of culture-independent and culture-dependent methods as well microscopic techniques. Scanning electron microscopy (SEM) revealed that the microflora on three storeroom objects were characterized by a marked presence of Eurotium halophilicum. Real-time quantitative polymerase chain reaction (qPCR) analysis proved that fungi were the main causative agents behind the biodeterioration in this case. Fungal internal transcribed spacer (ITS) amplicon sequencing documented the presence of two main fungi — Eurotium halophilicum and Aspergillus penicillioides. Molecular identification of fungal strains isolated from the surfaces and the air of the storeroom were most closely related to Chaetomium, Aspergillus, Penicillium, and Fusarium, showing discrepancies in fungal taxa compared to ITS amplicon sequencing. The most isolated bacterial phylum was Firmicutes, mostly Bacillus members. In addition, four biocide products — Preventol^® D 7, P 91, 20 N and Euxyl^® K 100 were selected to test their capability against fungal strains isolated from the surfaces. According to the susceptibility assay, Preventol^® D 7 based on isothiazolinones was the most effective against fungal isolates. Findings from this study provided a knowledge about storeroom fungi, and exemplify a type of preliminary test that may be conducted before planning any biocide treatment, which may be useful to mitigate the fungal deterioration for further conservation of the museum.

Microbial diversity in biodeteriorated Greek historical documents dating back to the 19th and 20th century: A case study

Paper documents in archives, libraries, and museums often undergo biodeterioration by microorganisms. Fungi and less often bacteria have been described to advance paper staining, so called “foxing” and degradation of paper substrates. In this study, for the first time, the fungal and bacterial diversity in biodeteriorated paper documents of Hellenic General State Archives dating back to the 19th and 20th century has been assessed by culture‐dependent and independent methods. The internally transcribed spacer (ITS) region and 16S rRNA gene were amplified by PCR from fungal and bacterial isolates and amplicons were sequenced. Sequence analysis and phylogeny revealed fungal phylotypes like Penicillium sp., Cladosporium sp., Penicillium citrinum, Alternaria infectoria, Alternaria alternata, Epicoccum nigrum, and Penicillium chrysogenum which are often implicated in paper deterioration. Bacterial phylotypes closely related to known biodeteriogenic bacteria such as Bacillus spp., Micrococcus spp., Kocuria sp. in accordance with previous studies were characterized. Among the fungal phylotypes described in this study are included well‐known allergens such as Penicillium spp., Alternaria spp., and Cladosporium spp. that impose a serious health threat on staff members and scholars. Furthermore, fungal isolates such as Chalastospora gossypii and Trametes ochracea have been identified and implicated in biodeterioration of historical paper manuscripts in this study for the first time. Certain new or less known fungi and bacteria implicated in paper degradation were retrieved, indicating that particular ambient conditions, substrate chemistry, or even location might influence the composition of colonizing microbiota.

Identification of mycotoxins by UHPLC-QTOF MS in airborne fungi and fungi isolated from industrial paper and antique documents from the Archive of Bogotá

Mold deterioration of historical documents in archives and libraries is a frequent and complex phenomenon that may have important economic and cultural consequences. In addition, exposure to toxic fungal metabolites might produce health problems. In this work, samples of broths of fungal species isolated from the documentary material and from indoor environmental samples of the Archive of Bogotá have been analyzed to investigate the presence of mycotoxins. High resolution mass spectrometry made possible to search for a large number of mycotoxins, even without reference standards available at the laboratory. For this purpose, a screening strategy based on ultra-high pressure liquid chromatography coupled to quadrupole-time of flight mass spectrometry (UHPLC-QTOF MS) under MS(E) mode was applied. A customized home-made database containing elemental composition for around 600 mycotoxins was compiled. The presence of the (de)protonated molecule measured at its accurate mass was evaluated in the samples. When a peak was detected, collision induced dissociation fragments and characteristic isotopic ions were also evaluated and used for tentative identification, based on structure compatibility and comparison with literature data (if existing). Up to 44 mycotoxins were tentatively identified by UHPLC-QTOF MS. 34 of these tentative compounds were confirmed by subsequent analysis using a targeted LC-MS/MS method, supporting the strong potential of QTOF MS for identification/elucidation purposes. The presence of mycotoxins in these samples might help to reinforce safety measures for researchers and staff who work on reception, restoration and conservation of archival material, not only at the Archive of Bogotá but worldwide.

Amid the possible causes of a very famous foxing: molecular and microscopic insight into Leonardo da Vinci's self-portrait

Leonardo da Vinci's self-portrait is affected by foxing spots. The portrait has no fungal or bacterial infections in place, but is contaminated with airborne spores and fungal material that could play a role in its disfigurement. The knowledge of the nature of the stains is of great concern because future conservation treatments should be derived from scientific investigations. The lack of reliable scientific data, due to the non-culturability of the microorganisms inhabiting the portrait, prompted the investigation of the drawing using non-invasive and micro-invasive sampling, in combination with scanning electron microscope (SEM) imaging and molecular techniques. The fungus Eurotium halophilicum was found in foxing spots using SEM analyses. Oxalates of fungal origin were also documented. Both findings are consistent with the hypothesis that tonophilic fungi germinate on paper metabolizing organic acids, oligosaccharides and proteic compounds, which react chemically with the material at a low water activity, forming brown products and oxidative reactions resulting in foxing spots. Additionally, molecular techniques enabled a screening of the fungi inhabiting the portrait and showed differences when different sampling techniques were employed. Swabs samples showed a high abundance of lichenized Ascomycota, while the membrane filters showed a dominance of Acremonium sp. colonizing the drawing.

Microbiological Analysis of Surfaces of Leonardo Da Vinci's Atlantic Codex: Biodeterioration Risk

Following the discovery of discoloration on some pages of the Atlantic Codex (AC) of Leonardo da Vinci kept in the Biblioteca Ambrosiana in Milan, some investigations have been carried out to verify the presence of microorganisms, such as bacteria and fungi. To verify the presence of microorganisms a noninvasive method of sampling has been used that was efficient and allowed us to highlight the microbial facies of the material that was examined using conventional microbiological techniques. The microclimatic conditions in the storage room as well as the water content of the volume were also assessed. The combined observations allowed the conclusion that the discoloration of suspected biological origin on some pages of AC is not related to the presence or current attack of microbial agents.

Assessing the microbiological risk to stored sixteenth century parchment manuscripts: a holistic approach based on molecular and environmental studies

The microbial risk for the conservation of seven sixteenth century parchment manuscripts, which showed brown discolouration putatively caused by microorganisms, was evaluated using non-invasive sampling techniques, microscopy, studies of surface-associated and airborne microflora with culture-independent molecular methods, and by measuring repository thermo-hygrometric values. Microscopic observations and ATP assays demonstrated a low level of contamination, indicating that the discolouration was not related to currently active microbial colonisation. Nevertheless, a culture-independent molecular approach was adopted to fully characterise surface-associated communities searching for biodeteriogens that could grow under appropriate thermo-hygrometric conditions. Indeed, potential biodeteriogens and microorganisms that are ecologically related to humans were found, suggesting the need to control the conservation environment and improve handling procedures. Microbial loads of air and thermo-hygrometric measurements showed that the repository was not suitable for preventing the microbial deterioration of parchment. A holistic approach to the assessment of risk of microbial deterioration of documents and heritage preservation is proposed for the first time.

Mineral-microbe interactions: biotechnological potential of bioweathering

Mineral-microbe interaction has been a key factor shaping the lithosphere of our planet since the Precambrian. Detailed investigation has been mainly focused on the role of bioweathering in biomining processes, leading to the selection of highly efficient microbial inoculants for the recovery of metals. Here we expand this scenario, presenting additional applications of bacteria and fungi in mineral dissolution, a process with novel biotechnological potential that has been poorly investigated. The ability of microorganisms to trigger soil formation and to sustain plant establishment and growth are suggested as invaluable tools to counteract the expansion of arid lands and to increase crop productivity. Furthermore, interesting exploitations of mineral weathering microbes are represented by biorestoration and bioremediation technologies, innovative and competitive solutions characterized by economical and environmental advantages. Overall, in the future the study and application of the metabolic properties of microbial communities capable of weathering can represent a driving force in the expanding sector of environmental biotechnology.