Abstract Groundwater ecosystems host diverse and complex microbial communities that play important roles in the biogeochemical processing of organic matter and in the maintenance of drinking water quality. Here we investigated the microbial community in suspended particulate matter (SPM) of biogeochemically distinct groundwaters (Hainich Critical Zone Exploratory) by analyzing branched and isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) from bacteria and archaea, respectively. The contributions of those lipids derived from dead and living organisms were determined by analyses of the core lipid distributions of core and intact polar GDGTs. We compared the groundwater GDGT distributions to the ones from soils of potential recharge areas and with archaeal 16S rRNA-gene based community reconstructions to estimate their origin in these terrestrial subsurface environments and thus their potential use for evaluating soil inputs into groundwater. In soils, the relative abundance of intact polar branched GDGTs (brGDGTs) was lower than that of isoprenoid GDGTs (isoGDGTs; 2% vs 5% of total GDGTs), while the opposite trend (71% vs 22% of total GDGTs) was observed in the core lipid pools. This supports previous observations that soil brGDGT-producing bacteria might be more active and thus have higher regeneration rates than the isoGDGT-producing archaea. We found similar trends in the groundwater that might indicate higher activity (i.e., cell division) of brGDGT-producing bacteria than of isoGDGT-producing archaea. The higher relative abundance of the hexamethylated brGDGT in the groundwater SPM (mean 65 ± 9%, n = 5) than in soils (mean 16 ± 7%, n = 22) indicated an in situ origin of brGDGT-producing bacteria. Higher contributions of penta- and tetra-methylated brGDGTs, which suggested some inputs from soil bacteria, was only detected in two out of seven groundwater samples. The strong correlation between core and intact polar isoGDGTs (R2 = 0.99, n = 7) in groundwater SPM indicated low disturbance (e.g., surface inputs) and suggested indigenous archaeal communities in the groundwater. This was supported by the results from a previous 16S rRNA-gene study that detected distinct archaeal groups in soils and groundwater. This first GDGT study in groundwater demonstrated that even dynamic karstic subsurface environments host an indigenous bacterial and archaeal community that is adapted to the living conditions. Furthermore, fast recharge events are likely detectable using tetraether lipids from the soil microbial community.

中文翻译：

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地下水中核心和完整细菌和古菌四醚脂质的原位生产

摘要 地下水生态系统拥有多样化和复杂的微生物群落，它们在有机物的生物地球化学处理和饮用水质量的维持中发挥着重要作用。在这里，我们通过分析分别来自细菌和古细菌的支链和类异戊二烯甘油二烷基甘油四醚 (GDGT)，研究了生物地球化学不同的地下水（Hainich 临界区探索）的悬浮颗粒物 (SPM) 中的微生物群落。通过对核心和完整极性 GDGT 的核心脂质分布进行分析，确定了来自死生物和活生物体的那些脂质的贡献。我们将地下水 GDGT 分布与潜在补给区土壤的分布以及基于古菌 16S rRNA 基因的群落重建进行了比较，以估计它们在这些陆地地下环境中的起源，从而估计它们在评估土壤对地下水的输入方面的潜在用途。在土壤中，完整极性分支 GDGT (brGDGT) 的相对丰度低于类异戊二烯 GDGT（isoGDGT；占总 GDGT 的 2% 对 5%），而观察到相反的趋势（占总 GDGT 的 71% 对 22%）在核心脂质池中。这支持先前的观察，即土壤产生 brGDGT 的细菌可能比产生 isoGDGT 的古细菌更活跃，因此具有更高的再生率。我们在地下水中发现了类似的趋势，这可能表明活动较高（即，细胞分裂）产生 brGDGT 的细菌比产生 isoGDGT 的古细菌。地下水 SPM 中六甲基化 brGDGT 的相对丰度（平均 65 ± 9%，n = 5）高于土壤（平均 16 ± 7%，n = 22），表明产 brGDGT 细菌的原位来源。五甲基化和四甲基化 brGDGT 的更高贡献，这表明一些来自土壤细菌的输入，仅在七分之二的地下水样品中检测到。地下水 SPM 中核心和完整极地 isoGDGT（R2 = 0.99，n = 7）之间的强相关性表明低干扰（例如，地表输入）并表明地下水中存在土著古菌群落。这得到了先前 16S rRNA 基因研究结果的支持，该研究在土壤和地下水中检测到不同的古菌群。地下水中的第一个 GDGT 研究表明，即使是动态岩溶地下环境也拥有适应生活条件的本土细菌和古菌群落。此外，使用来自土壤微生物群落的四醚脂质可能会检测到快速充电事件。