Table 5_Metagenomic inference of microbial community composition and function in the weathering crust aquifer of a temperate glacier.xlsx

Bacterial, fungal, and algal communities that colonize aquatic systems on glacial ice surfaces mediate biogeochemical reactions that alter meltwater composition and affect meltwater production and storage. In this study, we sought to improve understanding of microbial communities inhabiting the shallow aquifer that forms seasonally within the ice surface of a glacier’s ablation zone (i.e., the weathering crust aquifer). Using a metagenomic approach, we compared gene contents of microbial assemblages in the weathering crust aquifer (WCA) of the Matanuska Glacier (Alaska, USA) to those recovered from supraglacial features and englacial ice. High abundances of Pseudomonadota, Cyanobacteriota, Actinomycetota, and Bacteroidota were observed across all samples, while taxa in class Gammaproteobacteria were found at significantly higher abundances in the weathering crust aquifer. The weathering crust aquifer samples also contained higher abundances of Dothideomycetes and Microbotryomyetes; fungal classes commonly observed in snow and other icy ecosystems. Phylogenetic analysis of 18S rRNA and rbcL gene sequences indicated high abundances of algae in the WCA that are closely related (> 98% and > 93% identity, respectively) to taxa of Ancylonema (Streptophyta) and Ochromonas (Ochrophyta) reported from glacial ice surfaces in Svalbard and Antarctic sea ice. Many functional gene categories (e.g., homeostasis, cellular regulation, and stress responses) were enriched in samples from the weathering crust aquifer compared to those from proximal englacial and supraglacial habitats, providing evidence for ecological specialization in the communities. The identification of phagotrophic phytoflagellate taxa and genes involved in mixotrophy implies that combined phototrophic and heterotrophic production may assist with persistence in the low light, low energy, and ephemeral conditions of the weathering crust environment. The compositional and functional differences we have documented indicate distinct microbial distributions and functional processes occur in the weathering crust aquifer environment, and we discuss how deciphering these nuances is essential for developing a more complete understanding of ecosystem biogeochemistry in supraglacial hydrological systems.

冰面上的水生系统被细菌、真菌和藻类群落所占据，这些群落介导的地球生物化学作用改变了融水成分，并影响融水的生成和储存。在本研究中，我们旨在提高对栖息于冰川消融区冰面季节性形成的浅层地下水（即风化壳地下水）中微生物群落的理解。采用宏基因组学方法，我们将来自阿拉斯加马图纳斯卡冰川（美国）风化壳地下水（WCA）的微生物群落的基因组成与来自冰上特征和冰内冰的微生物组成进行了比较。在所有样本中均观察到Pseudomonadota、Cyanobacteriota、Actinomycetota和Bacteroidota的高丰度，而在风化壳地下水中，Gammaproteobacteria类群的丰度显著较高。风化壳地下水样本还含有较高丰度的Dothideomycetes和Microbotryomyetes；这些真菌类群通常在雪和其他冰冻生态系统中观察到。通过对18S rRNA和rbcL基因序列的系谱分析，发现WCA中藻类的丰度较高，分别与斯瓦尔巴德和南极海冰表面的Ancylonema（Streptophyta）和Ochromonas（Ochrophyta）类群（>98%和>93%的同源性）密切相关。与邻近的冰内和冰上生境相比，风化壳地下水样本中富集了许多功能基因类别（例如，稳态、细胞调节和应激反应），这为该群落生态学上的专业化提供了证据。发现摄食性植物鞭毛虫类群和参与混食的基因，表明结合光合作用和异养生产的能量可能有助于在风化壳环境中低光照、低能量和短暂条件下维持生存。我们所记录的组成和功能差异表明，在风化壳地下水环境中存在独特的微生物分布和功能过程，我们讨论了阐明这些细微差别对于全面理解冰川水文系统中生态系统地球生物化学的重要性。