Innovative approaches for the processes involved in microbial biodeterioration of cultural heritage materials

Fungal biodeterioration and preservation of cultural heritage, artwork, and historical artifacts: extremophily and adaptation

SUMMARYFungi are ubiquitous and important biosphere inhabitants, and their abilities to decompose, degrade, and otherwise transform a massive range of organic and inorganic substances, including plant organic matter, rocks, and minerals, underpin their major significance as biodeteriogens in the built environment and of cultural heritage. Fungi are often the most obvious agents of cultural heritage biodeterioration with effects ranging from discoloration, staining, and biofouling to destruction of building components, historical artifacts, and artwork. Sporulation, morphological adaptations, and the explorative penetrative lifestyle of filamentous fungi enable efficient dispersal and colonization of solid substrates, while many species are able to withstand environmental stress factors such as desiccation, ultra-violet radiation, salinity, and potentially toxic organic and inorganic substances. Many can grow under nutrient-limited conditions, and many produce resistant cell forms that can survive through long periods of adverse conditions. The fungal lifestyle and chemoorganotrophic metabolism therefore enable adaptation and success in the frequently encountered extremophilic conditions that are associated with indoor and outdoor cultural heritage. Apart from free-living fungi, lichens are a fungal growth form and ubiquitous pioneer colonizers and biodeteriogens of outdoor materials, especially stone- and mineral-based building components. This article surveys the roles and significance of fungi in the biodeterioration of cultural heritage, with reference to the mechanisms involved and in relation to the range of substances encountered, as well as the methods by which fungal biodeterioration can be assessed and combated, and how certain fungal processes may be utilized in bioprotection.

Biomineral deposits and coatings on stone monuments as biodeterioration fingerprints

Biominerals deposition processes, also called biomineralisation, are intimately related to biodeterioration on stone surfaces. They include complex processes not always completely well understood. The study of biominerals implies the identification of organisms, their molecular mechanisms, and organism/rock/atmosphere interactions. Sampling restrictions of monument stones difficult the biominerals study and the in situ demonstrating of biodeterioration processes. Multidisciplinary works are required to understand the whole process. Thus, studies in heritage buildings have taken advantage of previous knowledge acquired thanks to laboratory experiments, investigations carried out on rock outcrops and within caves from some years ago. With the extrapolation of such knowledge to heritage buildings and the advances in laboratory techniques, there has been a huge increase of knowledge regarding biomineralisation and biodeterioration processes in stone monuments during the last 20 years. These advances have opened new debates about the implications on conservation interventions, and the organism's role in stone conservation and decay. This is a review of the existing studies of biominerals formation, biodeterioration on laboratory experiments, rocks, caves, and their application to building stones of monuments.

Biofilm colonization of stone materials from an Australian outdoor sculpture: Importance of geometry and exposure

The safeguarding of Australian outdoor stone heritage is currently limited by a lack of information concerning mechanisms responsible for the degradation of the built heritage. In this study, the bacterial community colonizing the stone surface of an outdoor sculpture located at the Church of St. John the Evangelist in Melbourne was analysed, providing an overview of the patterns of microbial composition associated with stone in an anthropogenic context. Illumina MiSeq 16S rRNA gene sequencing together with confocal laser microscope investigations highlighted the bacterial community was composed of both phototrophic and chemotrophic microorganisms characteristic of stone and soil, and typical of arid, salty and urban environments. Cardinal exposure, position and surface geometry were the most important factors in determining the structure of the microbial community. The North-West exposed areas on the top of the sculpture with high light exposure gave back the highest number of sequences and were dominated by Cyanobacteria. The South and West facing in middle and lower parts of the sculpture received significantly lower levels of radiation and were dominated by Actinobacteria. Proteobacteria were observed as widespread on the sculpture. This pioneer research provided an in-depth investigation of the microbial community structure on a deteriorated artistic stone in the Australian continent and provides information for the identification of deterioration-associated microorganisms and/or bacteria beneficial for stone preservation.

Bats, monkeys and plants in the time of Covid-19 pandemic at Angkor monuments

Knowledge of biodeterioration and protection of cultural heritage depends on the scientific understanding of the substratum materials, the ambient environment, the fauna and flora including the microorganisms so an overall picture can be constructed to serve as a basis for protection and management. Over the past more than 20 years of survey and research, an accumulated dataset is available on the mechanisms on the (bio)deterioration of stone monuments in Cambodia, involving interactions among water cycling and salt dynamics with the presence of a rich surface microbiome, the biofilms. However, during the Covid-19 period (2020-2022), because of a drastic drop on tourist population, the number of bats and monkeys are on the rising, which have an impact on the on-going protection efforts. At the same time, large trees around and on the cultural heritage sites are being managed by trimming and removal to decrease the potential risk and negative impacts from them. The new management scheme needs scientific results for the long-term successful protection of these cultural heritage. A close examination of these issues is also meaningful and important to the research new initiatives and policy to be implemented not only in Cambodia but also elsewhere.

Unraveling disparate roles of organisms, from plants to bacteria, and viruses on built cultural heritage

The different organisms, ranging from plants to bacteria, and viruses that dwell on built cultural heritage can be passive or active participants in conservation processes. For the active participants, particular attention is generally given to organisms that play a positive role in bioprotection, bioprecipitation, bioconsolidation, bioremediation, biocleaning, and biological control and to those involved in providing ecosystem services, such as reducing temperature, pollution, and noise in urban areas. The organisms can also evolve or mutate in response to changes, becoming tolerant and resistant to biocidal treatments or acquiring certain capacities, such as water repellency or resistance to ultraviolet radiation. Our understanding of the capacities and roles of these active organisms is constantly evolving as bioprotection/biodeterioration, and biotreatment studies are conducted and new techniques for characterizing species are developed. This brief review article aims to shed light on interesting research that has been abandoned as well as on recent (some ongoing) studies opening up new scopes of research involving a wide variety of organisms and viruses, which are likely to receive more attention in the coming years. KEY POINTS: • Organisms and viruses can be active or passive players in heritage conservation • Biotreatment and ecosystem service studies involving organisms and viruses are shown • Green deal, health, ecosystem services, and global change may shape future research.

A Short Overview of Recent Developments in the Application of Polymeric Materials for the Conservation of Stone Cultural Heritage Elements

Stones are ones of the most ancient natural materials exploited by humans, with different uses, from tools to buildings, that have endured over time in better conditions than other objects belonging to cultural heritage. Given the importance of those silent witnesses of our past, as well as our duty to preserve all parts of cultural heritage for future generations, much effort was put into the development of materials for their consolidation, protection, self-cleaning, or restoration. Protection of ancient stone monuments and objects has gained the interest of researchers in the last decades in the field of conservation of cultural heritage. In this respect, the present paper aims to be a critical discussion regarding potential polymeric materials, which can be used in restorative and conservative approaches for stone materials of cultural heritage importance, against physical degradation phenomena. Recent advances in this area are presented, as well as the current bottle-necks and future development perspectives.

Biodeterioration Assessment of a Unique Old Pharaonic Kingdom Wooden Statue Using Advanced Diagnostic Techniques

A recently discovered Egyptian wooden statue of King Djedefre was studied together with some surrounding burial soil samples for assessing the statue biodeterioration. The wooden morphological characterisation identified the hardwood Acacia nilotica as the wood type. X-ray diffraction, micro-FT-IR spectroscopy, and scanning electron microscopy with an X-ray spectrometer were used to evaluate the wood deterioration degree and the soil contribution in wood biodeterioration. Microbiological analyses (fluorescent in situ hybridisation and polymerase chain reaction) were also performed to detect the microbial attack on the statue. The prolonged interaction of the statue with the burial environment caused a strong wood decay due to biotic (fungi and bacteria) and abiotic factors (e.g., humidity fluctuations of the burial environment), which caused the severe cracking and collapsing of the wood structures. The analyses of the burial soil mineral composition were relevant for obtaining an overall picture of the statue deterioration. The results are useful for planning the right conservation procedures for this very particular and important wooden statue. Furthermore, analysis of the woody cell wall will help in the selection of appropriate consolidation and recovery treatments. Because the statue is a unique single piece of wood, and the morphological observations indicated that it is a bald woman in a sitting position, this statue will provide new and interesting knowledge of Egyptian culture.

Biofilms on stone monuments: biodeterioration or bioprotection?

Debate on whether biofilms on stone monuments are biodeteriorative or bioprotective is long-standing. We propose a criterion of 'relative bioprotective ratio' for assessing the ambivalent role of the biofilms by comparing biodeterioration with weathering. A boundary between biodeterioration and bioprotection exists and fluctuates with dynamic microflora influenced by environmental conditions.