## 4 Discussion
### Biocide Discussion  
The results of biocide products provide preliminary knowledge about the susceptibility of lacquerware fungi to four commercial biocides. According to these data, one may think that a biocide application based on an active compound like isothiazolione could be a useful method to control fungal biodeterioration, and commercial biocide products based on isothiazolione have been widely used on paper objects and stone cultural heritage monuments [36; 37; 38; 39]. However, there are few studies on their long-term efficacy, and the potential recolonization after biocide application has not been monitored [36]. In the worst case, microbial communities may develop resistance to these biocides, and might become even more harmful to the objects [40; 41]. In addition, under the selective pressure of biocides, microorganisms previously absent may replace the original microbial communities, leading to new microbial outbreaks [36]. The outbreak of the fungi _F. solani_ species complex of Lascaux Cave in France is a precedent. Biocides, such as benzalkonium chloride (BC), were used to control this outbreak between 2001 and 2004 [21]. Four months after the initial application, some black stains progressively invaded the cave, marking a new outbreak. Besides, years of BC application have selected resistance populations, including a mix of _Ralstonia_ and _Pseudomonas_, as well as free-living amoebae [20; 21; 42]. As suggested by [PERSON] et al., it is necessary to weigh the pros and cons of using biocides in each specific environment. Furthermore, any biocide treatment should be carefully designed even if it may be difficult, which includes not also laboratory assays like this study, but also field assays in the real environment [21].  
We believe that the choice of biocides is also very important. BC has been used as an antifungal agent against fungi isolated from cultural heritage. The biological activity of BC is ascribed to its quaternary ammonium group [43]. However, microorganisms tend to develop resistance to quaternary ammonium compounds (QACs), resulting in microorganisms colonizing surfaces treated with QACs for a long period [44]. It has been suggested that use of nitrogen-containing biocides should be avoidedbecause they enable several groups of micro- and macro-organisms to use it as a nitrogen source favoring recolonization [45]. The main active ingredients of the biocides we used is isothiazolinone, which is relatively environmentally friendly and efficient. A study isolated some fungi species from the stuccos of the vault of a religious building in Torino (NW-Italy), and evaluated the sensitivity of the fungi species to widely used biocidal products [46]. As a result BC, in the low range of recommended concentrations (0.25%) was demonstrated ineffective against most of the tested fungal strains, while isothiazolinone-containing biocides displayed the best effectiveness against all the strains. Based on the above considerations and our experimental results, we focused on the effect of isothiazolinone-containing biocides. However, its effects on wooden lacquerware still requires evaluation.  
In the museum, the fungal contamination of lacquerware is low. To avoid breaking the relatively stable current balance, commercial biocides should not be used at the present stage. For the conservation of these wood lacquers, they should be preserved at low temperature to control fungal deterioration. Moreover, the stored water could be replaced with sterile water to avoid fungal colonization. Alternatively, continuous monitoring of the fungal community is also necessary. Once there is a significant fungal outbreak, physical, not chemical cleaning methods should be considered first, such as careful mechanical removal of fungal biomass and so on.