## 5 Summary and Future Perspectives  
Current research addressing the issue of biodeterioration of cultural heritage needs to focus on sampling methods and appropriate analytical techniques used afterward. Application of non-invasive/non-destructive sampling strategies is required in microbiological studies for conservation. The NGS-based metagenomics and metatransriptomics should be applied to the study of biodeterioration of cultural heritage for the microbial structure (especially spatial distribution structure) of the microbiome and the potential of specific microbial groups and microbe-mediated transformation processes contributing to biodeterioration. The NGS-based results can provide sound basis for the purpose-driven biochemical functional analysis or develop enrichment and culturing strategies to isolate the implicated groups of microorganisms with significant roles in biodeterioration. There are apparent challenges for investigations to develop the purpose-specific biochemical functional analysis for measuring the valid deterioration effects of microbiome and for enhancing knowledge of cultivation of microorganisms from a specific material.  
Delineation of the processes and mechanisms involved for (bio)deterioration should be the basis for understanding the current status with a selective cultural heritage. When the destructive reactions are known and also the specific microorganisms responsible for the processes, remediation strategies and management plan can be proposed accordingly [94]. Sulfur-driving acid production can be dealt with from restriction on fuel quality and air quality mandate in policy and management while intervention on site can be carried out through mineralization to immobilize produced SO4\({}^{2-}\). NO3\({}^{-}\) is an issue that is more difficult to address than SO4\({}^{2-}\), but an effective way to deal with it should be to focus on the source of NH4\({}^{+}\) to eliminate its contribution from the beginning. In addition, new emerging science on materials can also take an important role in the effective protection and management of culture heritage to decrease the detrimental contribution from microorganisms and their biochemical capabilities. Overall, protection of cultural heritage is a complex subject and synergies of different subjects will contribute to the advancement of this field for both basic knowledge and also applications.  
Conceptualization, W.L. and J.-D.G.; writing--original draft preparation, X.D.; writing--review and editing, X.D., W.L. and J.-D.G.; supervision, J.-D.G.; project administration and funding acquisition, W.L. and J.-D.G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Shenzhen Scientific Project Fund (JCYJ20170410103015603), and Hong Kong RGC GRF Grant (No. 17302119).  
This project was financially supported by Shenzhen Scientific Project Fund (JCYJ20170410103015603), and Hong Kong RGC GRF Grant (No. 17302119). We would like to thank the Apsara Authority of the Kingdom of Cambodia for permission to conduct sampling and research for more than a decade, [PERSON] for the SEM in Figure 1, and [PERSON] for help with the photographs presented in Figure 2.  
The authors declare no conflict of interest.