Fungi are an important component of microbial communities and are well known for their ability to decompose refractory, highly polymeric organic matter. In soils and aquatic systems, fungi play an important role in carbon processing, however, their diversity, community structure and function as well as ecological role, particularly in groundwater, are poorly studied. The aim of this study was to examine the fungal community composition, diversity and function in groundwater from 16 boreholes located in the vicinity of two lakes in NE Germany that are characterized by contrasting trophic status. The analysis of 28S rRNA gene sequences amplified from the groundwater revealed high fungal diversity and clear differences in community structure between the aquifers. Most sequences were assigned to Ascomycota and Basidiomycota, but members of Chytridiomycota, Cryptomycota, Zygomycota, Blastocladiomycota, Glomeromycota and Neocallimastigomycota were also detected. In addition, 27 species of fungi were successfully isolated from the groundwater samples and tested for their ability to decompose complex organic polymers – the predominant carbon source in the groundwater. Most isolates showed positive activities for at least one of the tested polymer types, with three strains, belonging to the genera Gibberella, Isaria and Cadophora, able to decompose all tested substrates. Our results highlight the high diversity of fungi in groundwater, and point to their important ecological role in breaking down highly polymeric organic matter in these isolated microbial habitats.

真菌是微生物群落的重要组成部分，以其分解难降解的高聚合有机物的能力而闻名。在土壤和水生系统中，真菌在碳加工中起着重要的作用，但是，对它们的多样性，群落结构和功能以及生态作用，尤其是在地下水中的作用研究很少。这项研究的目的是检查位于德国东北部两个湖泊附近的16个钻孔的地下水中真菌群落的组成，多样性和功能，其营养状况对比鲜明。从地下水中扩增出的28S rRNA基因序列的分析表明，较高的真菌多样性和含水层之间的群落结构存在明显差异。大多数序列分配给了子囊菌和担子菌菌，但是还检出了壶菌，隐孢子虫，合子菌，Blastocladiomycota，Glomeromycota和Neocallimastigomycota的成员。此外，从地下水样品中成功分离出27种真菌，并测试了它们分解复杂有机聚合物（地下水中主要碳源）的能力。大多数分离株对至少一种测试的聚合物类型表现出阳性活性，其中三种菌株属于该属赤，棒束孢和Cadophora，能分解所有测试底物。我们的结果突出了地下水中真菌的高度多样性，并指出了它们在分解这些孤立的微生物栖息地中的高聚合有机物方面的重要生态作用。