Essential oils as alternative biocides for the preservation of waterlogged archaeological wood

microorganisms Article Essential Oils as Alternative Biocides for the Preservation ofWaterlogged ArchaeologicalWood Federica Antonelli 1,* , Marco Bartolini 2, Marie-Laure Plissonnier 3 , Alfonso Esposito 4 , Giulia Galotta 2, Sandra Ricci 2, Barbara Davidde Petriaggi 5 , Cristian Pedone 6, Antonella Di Giovanni 6, Silvano Piazza 4,7 , Francesca Guerrieri 3,*,y and Manuela Romagnoli 1,y 1 Department for Innovation in Biological, Agro-Food and Forestry Systems (DIBAF), Tuscia University, 01100 Viterbo, Italy; mroma@unitus.it 2 Biology Laboratory, Istituto Centrale per il Restauro (ICR), Ministry of Cultural Heritage and Activities and Tourism (MIBACT), 00153 Rome, Italy; marco.bartolini@beniculturali.it (M.B.); giulia.galotta@beniculturali.it (G.G.); sandra.ricci@beniculturali.it (S.R.) 3 Epigenetics and Epigenomic of Hepatocellular Carcinoma, U1052, Cancer Research Center of Lyon (CRCL), 69424 Lyon CEDEX 03, France; marie-laure.plissonnier@inserm.fr 4 Department of Cellular, Computational and Integrative Biology–CIBIO, University of Trento, 38123 Trento, Italy; alfonso.esposito@unitn.it (A.E.); silvano.piazza@icgeb.org (S.P.) 5 Underwater Archaeological Operations Unit, Istituto Centrale per il Restauro (ICR), Ministry of Cultural Heritage and Activities and Tourism (MIBACT), 00153 Rome, Italy; barbara.davidde@beniculturali.it 6 Restoration Laboratory of Organic Excavation Materials, Istituto Centrale per il Restauro (ICR), Ministry of Cultural Heritage and Activities and Tourism (MIBACT), 00153 Rome, Italy; cristianpedone95@hotmail.com (C.P.); antonella.digiovanni@beniculturali.it (A.D.G.) 7 Computational Biology, International Centre for Genetic Engineering and Biotechnology, 34149 Trieste, Italy * Correspondence: fedantonelli@gmail.com (F.A.); francesca.guerrieri@inserm.fr (F.G.) y Authors contributed equally. Received: 19 October 2020; Accepted: 14 December 2020; Published: 16 December 2020 Abstract: Waterlogged archaeological wood is exposed to a high risk of biological degradation during the post-excavation phases of storage and restoration. For this reason, often biocides must be used to preserve wooden remains. In the present work three essential oils (cinnamon, wild thyme, and common thyme) were tested as possible alternative biocides to use in the preservation of waterlogged archaeological wood. The oils were first tested in vitro to establish the minimum inhibitory concentration (MIC) and to evaluate the biocidal activity on selected fungal strains. Then, the established MIC was applied on waterlogged archaeological wood samples and during an actual restoration treatment. The e ectiveness of the oils was evaluated through cultural analyses, ATP quantification, and next-generation sequencing. The results showed that the oils caused a significant decrease in the vitality of fungal mycelia grown in vitro and of the microbiota present in treated wood and storage water. Furthermore, an influence on the composition of the bacterial communities of treated wood samples was observed. Although further tests are needed to evaluate interferences with the materials used during restoration procedures, essential oils could be considered as a possible alternative to the currently used biocide. Keywords: cinnamon; wild thyme; common thyme; cultural analyses; ATP bioluminescence; NGS; minimum inhibitory concentration (MIC);WAW; archaeological wood biodegradation; archaeological wood restoration Microorganisms 2020, 8, 2015; www.mdpi.com/journal/microorganisms12n