## 1 Introduction  
Nanhai No. 1, a Chinese Song Dynasty shipwck, was discovered in 1987 near the Chuanshan archipelago in the South China Sea, Guangdong Province. In 2007, Nanhai No. 1 was salvaged and displayed in \"the Crystal Palace\" of the Guangdong Maritime Silk Road Museum. In 2012, archaeological excavation was officially started [1], and a large number of precious cultural relics such as gold, silver, bronze, iron, lacquer and porcelain were found in the wreck. The discovery of Nanhai No. 1 wreck is of great significance to Chinese underwater archaeology, and also provides important clues for the study of Maritime Silk Road. The hull and the cultural relics of Nanhai No.1 are the key protected objects. With the excavation of Nanhai No.1, the exposed area of the hull increases gradually. The cultural relics need to go through the process of desalination, desulfurization and iron removal, so they are soaked in a specific buffer for a long time [2]. Due to the high humidity and high temperature in the storage environment of Nanhai No. 1, and the fact that wooden cultural relics are natural organic matter, this provides suitable conditions for the growth and reproduction of microorganisms [3]. Microorganisms are very harmful to wooden relics. Some bacteria and fungi can destroy wood by degrading cellulose, hemicellulose and lignin. For example, the ability of microorganisms such as _Trichoderma viride_, _Trichoderma reesei_, _Bacteroides cellulosolvens_, _Bacteroides succinogenes_ to degrade cellulose has been reported [4]. This will cause structural and mechanical changes of wooden cultural relics, and cause irreversible impact on precious cultural artifacts [5; 6; 7]. The main microorganisms of Nanhai No. 1 isolated by our previous research group include: _Fusarium solanti_ NK-NH1 [8], _Bacillus tequilensis_ NK-NH5, _Bacillus megaterium_ NK-NH10, _Bacillus velezensis_ NK-NH11 [9] and _Scedosporium apiosperm_ NK-W1-3 [10]. In addition, we have recently identified bacteria on the hull and surrounding sea mud including _Bacillus_ sp. NK-NH15, _Bacillus_ sp. NK-NH16, _Bacillus_ sp. NK-NH17 (Table S1). At present, Euxyl(r) K100 is the main antimicrobial agent used in Nanhai No.1 microbial control. Although it can effectively inhibit the growth of microorganisms, it is a little harmful to the environment and human body. Methylchloroisothiazolinone (MCI) and methylisothiazolinone (MI), the main components of Euxyl(r) K100, are widely used in cosmetic products [11]. MI and MCI can cause allergic contact dermatitis [12]. At the same time, MI has a certain volatility; it will slowly volatilize into the air, affecting the surrounding environment, and then cause harm to the contacts [13]. Therefore, it is an important task to find environment-friendly and health-friendly antimicrobial agents. Plant-derived antimicrobial agents are relatively safe and friendly to the human body and environment [14; 15]. At present, there are many reports that plant-derived antimicrobial agents are used in the actual control of microbial diseases [16]. Our research goal is to apply plant-derived antimicrobial agents to the microbial control of the Nanhai No. 1 shipw. Cinnamaldehyde is the main component of cinnamon essential oil, which is a yellow oily liquid [17]. The antiinflammatory, antioxidation, antiulcer, antibacterial, hypoglycemic and hypolipidemic properties of cinnamaldehyde have been reported [18]. Cinnamaldehyde has been widely used in food, medicine, cosmetics and other fields [19]. Previous studies have shown that cinnamaldehyde has good inhibitory effect on _Aspergillus_, _Fusarium_, _Penicillium_, _Rhizopus_ and other fungi [20; 21; 22], _Escherichia coli_, _Bacillus subtilis_, _Staphylococcus_ spp. and other bacteria [23; 24]. In this study, we first tested the cellulose degradation ability of the main destructive microorganisms of Nanhai No. 1, then tested the inhibition effect of cinnamaldehyde on these main destructive microorganisms. In order to play a practical role in the microbial control of Nanhai No.