A Review on Sampling Techniques and Analytical Methods for Microbiota of Cultural Properties and Historical Architecture

World cultural heritage suffers from deterioration caused by both natural and anthropogenic processes, among which microorganisms are significantly involved. Among the key issues of this topic, sampling techniques and analytical methods for revealing the microbiome are fundamental to obtaining useful results for understanding the key players and processes involved, and also for effective protection and management of the cultural heritage for humanity. A non-invasive and non-destructive sampling method is required for sampling of cultural properties prior to further analysis of the microbiome. One example is illustrated in this article. For many years, culture-dependent methods had been used before the invention of polymerase-chain reaction (PCR) methods and, more recently, specifically high-throughput next generation sequencing (NGS). NGS reveals the whole microbial community composition and the active microorganisms from genomic DNA and RNA, respectively. The recovered environmental DNA and RNA from samples provide the information on microbial community and composition, and the active members and biochemical processes of the microbial attributes. It should be emphasized that the metabolically-active members of functional microflora in the biofilm or microbiome on cultural heritage must be determined and identified from the RNA-based analysis to gain a substantially important insight of the active biodeterioration processes and also the effectiveness of the conservation strategies. The importance of the culture-independent technique, based on NGS, is that it can be used in combination with the conventional culturing methods to guide the isolation and enrichment of new microorganisms to gain further biochemical insights to advance the role of the specific microbial groups for biodeterioration of cultural heritage. At the same time, effective restoration and maintenance strategies can be formulated for the protection of world cultural heritage.