Unraveling the microbiome of the Great Wall of China

The Great Wall of China, one of the most emblematic human heritage sites ever built, is largely covered by a living skin with a potentially distinct microbiome from bare wall surfaces. However, the structure and function of this microbiome remain virtually unknown, which hampers any effort to understand the impacts of this microbiome on the long-term conservation of the Great Wall. Here, we investigated the microbiome of the Great Wall at six sampling sites along a 600 km section, which stretches across arid and semiarid climates and is covered by a mosaic of biological soil crusts (biocrusts) and exposed wall surfaces. We hypothesized that these biocrusts could establish a unique microhabitat and support a microbiome with a community structure and functional potential distinct from those on bare walls, thereby modulating the biodeterioration processes affecting the Great Wall. Our findings revealed that biocrust-covered sections exhibited a 12%–62% increase in abundance, diversity, and co-occurrence network complexity for bacterial and fungal communities compared with bare walls. Further metagenomic analyses indicated that biocrust cover enhanced the abundance of overall functional genes and stress resistance pathways within the microbiome by 4%–15%, while decreasing the metabolic pathways linked to heritage biodeterioration. Aridity was an additional determinant of the microbiome. Our work serves as a critical step towards understanding the microbiome of the Great Wall, which contributes to conserving this unparalleled human monument for future generations.作为人类有史以来建造的最具标志性的文化遗产之一，中国长城的主体表面被一层“活肤层”所覆盖，其微生物组（microbiome）与裸露的城墙表面存在显著差异。然而，该微生物组的结构与功能至今仍几乎未被探明，这极大阻碍了学界解析其对长城长期保护的影响机制。本研究沿横跨干旱与半干旱气候区的600公里长城区段，于6个采样点开展长城微生物组调查；该区域地表呈现生物土壤结皮（biological soil crusts，简称biocrusts）与裸露城墙表面镶嵌分布的格局。我们提出假说：此类生物土壤结皮可形成独特的微生境，支撑起群落结构与功能潜能均区别于裸露墙面的微生物组，进而调控影响长城的生物劣化（biodeterioration）过程。研究结果显示，相较于裸露墙面，覆盖生物土壤结皮的区段中细菌与真菌群落的丰度、多样性及共现网络复杂度均提升12%~62%。进一步的宏基因组（metagenomic）分析表明，生物土壤结皮的覆盖使微生物组内整体功能基因与抗逆通路的丰度提升4%~15%，同时降低了与文化遗产生物劣化相关的代谢通路丰度。干旱程度是影响微生物组的另一决定性因素。本研究为解析长城微生物组迈出了关键一步，有助于保护这一无与伦比的人类历史丰碑，造福后世子孙。