Biological growth represents one of the main threats for the conservation of subterranean cultural heritage. Knowledge of the conditions which favour the various taxonomic groups is important in delineating their control methods. Combining our experience regarding hypogea in Italy and the Republic of Korea, we aim to perform a critical review and comparison of the Biodeterioration Patterns (BPs) found, the materials used, and the conservative treatments applied. For this purpose, we focused on Etruscan tombs (Italy, 7th to 3th century BC) and the ancient tombs of the Baekje Dynasty (Republic of Korea, 6th to 7th centuries AD), most of which have been designated UNESCO World Heritage Sites, collecting original and bibliographic data as well as official documents. Results highlight the rich biodiversity of the bacterial and fungal species. Phototrophs were observed only in niches with sufficient light and the development of roots was also detected. Changes in humidity and temperature, the nature of the soil, nutrient accumulation, and vegetation above the hypogea along with human activities explain the different BPs. The effects of biocide treatments are also discussed, such as the emergence of dangerous fungal species. The shared data also enhance the role of overlaying tumuli and vegetation as well as protective barriers to reduce biological risk.

Wooden Cultural Heritage (WCH) represents a significant portion of the world’s historical and artistic heritage, consisting of immovable and movable artefacts. Despite the expertise developed since ancient times to enhance its durability, wooden artefacts are inevitably prone to degradation. Fungi play a pivotal role in the deterioration of WCH in terrestrial ecosystems, accelerating its decay and leading to alterations in color and strength. Reviewing the literature of the last 25 years, we aimed to provide a comprehensive overview of fungal diversity affecting WCH, the biochemical processes involved in wood decay, and the diagnostic tools available for fungal identification and damage evaluation. Climatic conditions influence the occurrence of fungal species in threatened WCH, characterized by a prevalence of wood-rot fungi (e.g., Serpula lacrymans, Coniophora puteana) in architectural heritage in temperate and continental climates and Ascomycota in indoor and harsh environments. More efforts are needed to address the knowledge fragmentation concerning biodiversity, the biology of the fungi involved, and succession in the degradative process, which is frequently centered solely on the main actors. Multidisciplinary collaboration among engineers, restorers, and life sciences scientists is vital for tackling the challenges posed by climate change with increased awareness. Traditional microbiology and culture collections are fundamental in laying solid foundations for a more comprehensive interpretation of big data.

Although subterranean tombs are largely protected from the external environment, the colonization of microorganisms threatens their conservation. Conventional biocides have negative effects on the environment, human health, and the sensitive materials in ancient tombs, especially painted murals. Therefore, we tested the biocidal effects of 11 plant-extracted essential oils (EOs) against two fungal strains and four bacterial strains isolated from Buyeo Royal Tomb No. 1, a World Heritage Site in South Korea. Oregano, clove bud, thyme, and cinnamon cassia EOs showed the highest antifungal and antibacterial activities. At concentrations suitable for practical application (3–10%), oregano and cinnamon cassia EOs exhibited the highest antifungal and antibacterial activities against the tested microbial strains. No variation in the surface properties and mineral composition was detected for the lithotype specimens (granite and gneiss) treated with the EOs at 1–10%. Low-concentration thyme and oregano EOs led to minimal color change in the painting layer specimens, whereas clove bud and cinnamon cassia EOs caused yellowing of the oyster shell white pigment at a concentration of 3–10%. Our results suggest that 3% oregano EO is a candidate biocide that could minimize the biological damage to and promote the conservation of ancient tomb murals.