Table_4_Epilithic Microbial Community Functionality in Deep Oligotrophic Continental Bedrock.XLSX

The deep terrestrial biosphere hosts vast sessile rock surface communities and biofilms, but thus far, mostly planktic communities have been studied. We enriched deep subsurface microbial communities on mica schist in microcosms containing bedrock groundwater from the depth of 500 m from Outokumpu, Finland. The biofilms were visualized using scanning electron microscopy, revealing numerous different microbial cell morphologies and attachment strategies on the mica schist surface, e.g., bacteria with outer membrane vesicle-like structures, hair-like extracellular extensions, and long tubular cell structures expanding over hundreds of micrometers over mica schist surfaces. Bacterial communities were analyzed with amplicon sequencing showing that Pseudomonas, Desulfosporosinus, Hydrogenophaga, and Brevundimonas genera dominated communities after 8–40 months of incubation. A total of 21 metagenome assembled genomes from sessile rock surface metagenomes identified genes involved in biofilm formation, as well as a wide variety of metabolic traits indicating a high degree of environmental adaptivity to oligotrophic environment and potential for shifting between multiple energy or carbon sources. In addition, we detected ubiquitous organic carbon oxidation and capacity for arsenate and selenate reduction within our rocky MAGs. Our results agree with the previously suggested interaction between the deep subsurface microbial communities and the rock surfaces, and that this interaction could be crucial for sustaining life in the harsh anoxic and oligotrophic deep subsurface of crystalline bedrock environment.

深部陆生生物圈孕育着庞大的固定岩石表面群落和生物膜，然而迄今为止，主要研究的是浮游生物群落。我们在微宇宙中富集了来自芬兰Outokumpu地区深度为500米的基岩地下水的云母片上的深层地下微生物群落。通过扫描电子显微镜对生物膜进行可视化，揭示了多种微生物细胞形态和附着策略在云母片表面，例如，具有外膜囊泡状结构的细菌、类似毛发的细胞外延伸物以及长达数百微米的管状细胞结构，这些结构在云母片表面扩展。通过扩增子测序分析细菌群落，发现假单胞菌属、脱硫杆菌属、氢杆菌属和短杆菌属在培养8-40个月后成为群落的主导菌属。从固定岩石表面宏基因组中组装了21个基因组，这些基因组中包含参与生物膜形成的基因，以及广泛的代谢特征，表明对寡营养环境的适应程度高，以及能在多种能量或碳源之间转换的潜力。此外，我们在岩石宏基因组中检测到了普遍存在的有机碳氧化以及砷酸盐和硒酸盐还原的能力。我们的结果与先前提出的深层地下微生物群落与岩石表面的相互作用相一致，并且这种相互作用对于维持结晶基岩环境中严酷的无氧和寡营养深层地下环境中的生命可能至关重要。