## 1 Introduction  
Ar Archaeological wood is defined as \"wood, used by an extinct human culture, that may or may not have been modified for or by use, and that was discarded by intent or accident into a specific natural environment\" [1]. Waterlogged archaeological wood (WAW) is characterized by a water filled structure and is recovered from water-saturated environments like sites submerged in lake, sea, river or wetland, or land waterlogged sites [2]. After recovery from the site and before museum display, any waterlogged archaeological wooden object must undergo restoration treatments aimed at consolidating the fragile material avoiding excessive dimensional changes or the wood collapse [3,4]. Depending on several factors like object dimension, wood level of degradation or availability of funds, the restoration operations and the phase preceding them may last for several months or even years. Like any organic material, wood is decomposed by biological processes in nature. In waterlogged sites where oxygen is limited, wood biodeterioration is mainly attributed to bacteria. These microorganisms are early colonizers of wood in wet environments, able to attack wood cell walls and pit membranes producing typical degradation patterns (e.g., erosion, tunneling, and cavitation) [5,6]. As long as wood is kept waterlogged, anaerobic or almost anaerobic conditions are maintained and the degradation processes are very slow. During excavation, storage phase, and restoration treatments, the oxygen level to which wooden artifacts are exposed rise and they can be subjected to faster decay forms attributed to fungi. Wood-degrading fungi cause three main types of decay: white, brown and soft rot. White and soft rot, caused respectively by basidiomycetes and ascomycetes/deuteromycetes, are the principal threat for waterlogged wood. By attacking cell wall polysaccharides and lignin, these fungi can lead to a more or less total destruction of wood in a relatively short time span [5, 6, 7, 8, 9, 10]. The colonization of WAW by bacteria and fungi has been widely studied to understand the degradation processes affecting this precious material [8,9, 11, 12, 13], but only little attention has been paid to the biological risk the wood is exposed to during excavation, storage, and/or restoration phases [7,10,14,15]. The study of wood biodeteriorogens and their degradative activity usually involves cultural and microscopic analyses [11,16, 11, 17, 18, 19, 20, 21]. Over the last decades, molecular techniques have been applied to this field of study. They were mainly based on the amplification and sequencing of DNA extracted from cultured microorganisms and, only in few cases, directly from wood [14,22, 23, 24, 25, 26]. Next-generation sequencing (NGS) is an innovative technique that was applied to the study of WAW conservation only in the last couple of years. Although five studies regarding the high-throughput sequencing of microbial communities involved in the biodeterioration of WAW were published [27, 28, 29, 30, 31], only two aimed to characterize the microorganisms present inside the wood. The other works focused on the analysis of the storage water and the burial environment or mainly aimed to characterize ancient DNA (aDNA) in order to perform evolutionary studies. The present work studied, through NGS, the bacterial and fungal communities present in WAW samples during the storage phase preceding the restoration to highlight the biological risk the wood is exposed to during this tricky period. The study involved different wood species coming from two archaeological land sites, the ancient port of Naples and San Rossoe in Pisa, and preserved in different conditions after recovery.