Hypogean or enclosed monuments are important cultural heritage sites that can suffer biodegradation. Many of the stone walls of the prestigious Domus Aurea are overwhelmed by dense biofilms and so need intervention. Room 93 was chosen as a study site with the aim to test the efficacy of phyto-derivatives as new biocides. Laboratory studies were performed comparing the effects of liquorice leaf extract (Glycyrrhiza glabra L.), lavender essential oil (Lavandula angustifolia Mill.) and a combination of both. In situ studies were also performed to test the effect of liquorice. The results were compared with those of the commonly used synthetic biocide benzalkonium chloride. The effects on the biofilms were assessed by microscopy along with chlorophyll fluorescence analysis. The phototrophs in the biofilms were identified morphologically, while the heterotrophs were identified with culture analysis and 16S gene sequencing. Results showed that the mixed solution liquorice/lavender was the most effective in inhibiting the photosynthetic activities of biofilms in the laboratory tests; while, in situ, the effect of liquorice was particularly encouraging as an efficient and low-invasive biocide. The results demonstrate a high potential biocidal efficacy of the phyto-derivatives, but also highlight the need to develop an efficient application regime.

The need for compatible materials for the preservation of cultural heritage has resulted in the revival of lime-based mortar technology and other applications. This work investigates the cohesion and integrity of lime mortars added with fresh mucilage extracted from five plants and evaluates their bioreceptivity for long-term durability. Specimens of lime mortars added with 2.5% of fresh mucilage extracted from Aloe vera, Cylindropuntia californica, Opuntia engelmannii, Opuntia ficus-indica and Salvia hispanica mucilages were analyzed for color change (colorimetry), cohesion (ultrasound measurements), integrity (X-rays) and bioreceptivity (microbiological tests).The internal structure of the specimens added with Cacti mucilages shows better compactness, and no color change was noticed in the bio-mortars also after aging. The bioreceptivity response of mortars inoculated with bacteria, fungi and a photosynthetic biofilm was quite different. Specimens added with Aloe and Cylindropuntia mucilages showed a higher extent of bioreceptivity than the control; the specimens of bio-mortars added with Opuntia engelmannii, Opuntia ficus-indica and Salvia hispanica mucilages did not appear, up to threemonths after the contamination, any microbial growth. These results indicate that the addition of mucilage improves the mortar qualities, but the choice of the plant mucilage must be carefully evaluated since it can be responsible for changes in the bioreceptivity of the mortar.

An understanding of the different microbial constellations or microbiomes, which every habitat and every organism harbor, will be the key to addressing many of the challenges humanity will face in the twenty-first century. Such comprehension could launch several innovations relating to natural and cultural capital, including historical and artistic heritage. In relation to cultural heritage, microorganisms are mainly known through their role as deteriogens, but the features creating damage can be exploited positively, attaining more sustainable restoration strategies, in accordance with the principles of compatibility and retreatability deriving from reflections on the Cultural Heritage inspired by the Charter of Venice (International charter for the Conservation and restoration of monument and sites (the Venice Chart 1964). In: ICOMOS, IInd International Congress of Architects and Technicians of Historic Monuments, 1964) onwards. In this article, we show a series of case studies, using both wild-type microorganisms and plant-based extracts, providing a comprehensive proof of concept of the feasibility of biotechnological solutions for a more sustainable restoration strategy, to replace the products in use which are often dangerous for operators, aggressive for works of art and no longer compatible with the environment. The overview of the case studies presented, many of which are still unpublished, responds to the need to go beyond the state of the art and has entirely sprung from suggestions by restorers, interested in learning about potential innovations and strongly determined to introduce non-toxic products in their daily work. In this perspective, the case studies dealt with two topics: bio-cleaning and disinfection. Noteworthy results were obtained on a platform of different types of artworks and different materials with compatible, harmless and selective products.