The current increase in public awareness of environmental risks is giving rise to a growth of interest in the microbiological safety of buildings. In particular, microbial proliferation on construction materials can be responsible for the degradation of indoor air quality that can increase health-risk to occupants. Raw earth materials are still widely used throughout the world and, in some cases, are linked to heritage habitats, as in the southwest of France. Moreover, these building materials are currently the subject of renewed interest for ecological and economic reasons. However, the microbial status of earthen materials raises major concerns: could the microbiome associated with such natural materials cause disease in building occupants? Very few analyses have been performed on the microbial communities present on these supports. Characterizing the raw earth material microbiome is also important for a better evaluation and understanding of the susceptibility of such materials to microbial development. This study presents the distribution of in situ bacterial and fungal communities on different raw earth materials used in construction. Various buildings were sampled in France and the microbial communities present were characterized by amplicon high-throughput sequencing (bacterial 16S rRNA gene and fungal ITS1 region). Bacterial culture isolates were identified at the species level by MALDI-TOF mass spectrometry. The major fungal and bacterial genera identified were mainly associated with conventional outdoor and indoor environmental communities, and no specific harmful bacterial species were detected on earthen materials. However, contrary to expectations, few human-associated genera were detected in dwellings. We found lower microbial alpha-diversity in earthen material than is usually found in soil, suggesting a loss of diversity during the use of these materials in buildings. Interestingly enough, the main features influencing microbial communities were building history and room use, rather than material composition. These results constitute a first in-depth analysis of microbial communities present on earthen materials in situ and may be considered as a first referential to investigate microbial communities on such materials according to environmental conditions and their potential health impact. The bacterial and fungal flora detected were similar to those found in conventional habitats and are thought to be mainly impacted by specific events in the building’s life, such as water damage.

中文翻译：

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与原位土质材料相关的微生物组的表征

当前公众对环境风险的意识增强，引起了人们对建筑物微生物安全性的关注。特别是，建筑材料上的微生物扩散可能导致室内空气质量下降，从而增加了居住者的健康风险。原料仍在世界范围内广泛使用，在某些情况下，与法国西南部的传统栖息地相关。此外，由于生态和经济原因，目前这些建筑材料引起了人们的关注。但是，土质材料的微生物状况引起了人们的极大关注：与这种天然材料相关的微生物组是否会引起建筑居民的疾病？对这些支持物上存在的微生物群落进行的分析很少。表征原材料的微生物组对于更好地评估和理解此类材料对微生物发育的敏感性也很重要。这项研究提出了建筑中使用的不同原材料上原位细菌和真菌群落的分布。在法国对各种建筑物进行了采样，并通过扩增子高通量测序（细菌16S rRNA基因和真菌ITS1区）对存在的微生物群落进行了表征。通过MALDI-TOF质谱法在物种水平上鉴定了细菌培养分离株。确定的主要真菌和细菌属主要与常规的室外和室内环境群落有关，在土质材料上未检测到特定的有害细菌。但是，与预期相反，在住宅中几乎没有发现与人类相关的属。我们发现土质材料中的微生物α多样性低于土壤中通常存在的微生物，表明在建筑物中使用这些材料时会丧失多样性。有趣的是，影响微生物群落的主要特征是建筑物的历史和房间使用情况，而不是材料组成。这些结果构成了对原位存在于土质材料上的微生物群落的首次深入分析，可被视为根据环境条件及其对健康的潜在影响调查此类物质上的微生物群落的第一参考。检测到的细菌和真菌菌群与常规栖息地中发现的细菌和真菌菌群相似，被认为主要受到建筑物生命中特定事件（例如水害）的影响。