Connectivity of Fennoscandian Shield terrestrial deep biosphere microbiomes with surface communities

The deep biosphere is an energy constrained ecosystem yet fosters diverse microbial communities that are key in biogeochemical cycling. Whether microbial communities in deep biosphere groundwaters are shaped by infiltration of allochthonous surface microorganisms or the evolution of autochthonous species remains unresolved. In this study, 16S rRNA gene amplicon analyses showed that few groups of surface microbes infiltrated deep biosphere groundwaters at the aspo Hard Rock Laboratory, Sweden, but that such populations constituted up to 49% of the microbial abundance. The dominant persisting phyla included Patescibacteria, Proteobacteria, and Epsilonbacteraeota. Despite the hydrological connection of the Baltic Sea with the studied groundwaters, infiltrating microbes predominantly originated from deep soil groundwater. Most deep biosphere groundwater populations lacked surface representatives, suggesting that they have evolved from ancient autochthonous populations. We propose that deep biosphere groundwater communities in the Fennoscandian Shield consist of selected infiltrated and indigenous populations adapted to the prevailing conditions.Westmeijer et al. employ high-throughput sequencing to investigate the connection between deep biosphere groundwaters and surface microbial communities. They suggest that the microbial communities of deep biosphere groundwaters in the Fennoscandian Shield are mostly comprised of autochthonous species, rather than migratory surface representatives

Diverse fractionation patterns of Rare Earth Elements in deep fracture groundwater in the Baltic Shield – Progress from utilisation of Diffusive Gradients in Thin-films (DGT) at the Äspö Hard Rock Laboratory

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Terrigenous dissolved organic matter persists in the energy-limited deep groundwaters of the Fennoscandian Shield

The deep terrestrial biosphere encompasses the life belowthe photosynthesisfueled surface that perseveres in typically nutrient and energy depleted anoxic groundwaters. The composition and cycling of this vast dissolved organic matter (DOM) reservoir relevant to the global carbon cycle remains to be deciphered. Here we show that recent Baltic Sea-influenced to ancient preHolocene saline Fennoscandian Shield deep bedrock fracture waters carried DOM with a strong terrigenous signature and varying contributions from abiotic and biotic processes. Removal of easily degraded carbon at the surfaceto-groundwater transition and corresponding microbial community assembly processes likely resulted in the highly similar DOM signatures across the notably different water types that selected for a core microbiome. In combination with the aliphatic character, depleted d13C signatures in DOM indicated recent microbial production in the oldest, saline groundwater. Our study revealed the persistence of terrestrially-sourced carbon in severely energy limited deep continental groundwaters supporting deep microbial life

Dissolved organic matter composition in the Fennoscandian Shield deep terrestrial biosphere (FT-ICR-MS), 2018 and 2019

Copious amounts of organic carbon are stored for long periods of time in deep continental groundwaters. Little is known about its composition and cycling, mainly due to the difficulties in obtaining sample material. Cool fracture waters of different origins can be obtained under clean conditions at Äspö Hard Rock Laboratory (Äspö HRL, Sweden), operated by the Swedish Nuclear Fuel and Waste Management Company (SKB). We sampled groundwater from different depth (171 to 507 meter below sea level) in the bedrock fractures in November 2018 and March-April 2019. We assessed water chemistry and dissolved organic matter composition via stable carbon isotopic and molecular-formula level analysis in recent Baltic Sea-influenced to old saline fracture waters in the granitic Fennoscandian shield. Molecular-level dissolved organic matter composition via Fourier-transform ion cyclotron resonance mass spectrometry using electrospray ionization in negative mode (FT-ICR-MS, 15 T Bruker Solarix) was done on solid-phase extracted (PPL) DOM extracts. Relative peak intensities from FT-ICR-MS with molecular formula attributions, elemental ratios and compound group classification of the final dataset are given. ICBM-Ocean was used for processing of FT-ICR mass spectra and formula attribution (Merder et al., 2020; doi:10.1021/acs.analchem.9b05659)

Water chemistry of unfiltered groundwater samples from the Fennoscandian Shield deep terrestrial biosphere in 2018 and 2019

Copious amounts of organic carbon are stored for long periods of time in deep continental groundwaters. Little is known about its composition and cycling, mainly due to the difficulties in obtaining sample material. Cool fracture waters of different origins can be obtained under clean conditions at Äspö Hard Rock Laboratory (Äspö HRL, Sweden), operated by the Swedish Nuclear Fuel and Waste Management Company (SKB). We sampled groundwater from different depth (171 to 507 meter below sea level) in the bedrock fractures in November 2018 and March-April 2019. We assessed water chemistry and dissolved organic matter composition via stable carbon isotopic and molecular-formula level analysis in recent Baltic Sea-influenced to old saline fracture waters in the granitic Fennoscandian shield. Physicochemical parameters, major ions, water isotopic compositions (δ18O and δD), total nitrogen as well as dissolved organic matter concentration and stable isotopic composition were obtained for unfiltered groundwater samples from different boreholes

Connectivity of Fennoscandian Shield terrestrial deep biosphere microbiomes with surface communities

The deep biosphere is an energy constrained ecosystem yet fosters diverse microbial communities that are key in biogeochemical cycling. Whether microbial communities in deep biosphere groundwaters are shaped by infiltration of allochthonous surface microorganisms or the evolution of autochthonous species remains unresolved. In this study, 16S rRNA gene amplicon analyses showed that few groups of surface microbes infiltrated deep biosphere groundwaters at the Äspö Hard Rock Laboratory, Sweden, but that such populations constituted up to 49% of the microbial abundance. The dominant persisting phyla included Patescibacteria, Proteobacteria, and Epsilonbacteraeota. Despite the hydrological connection of the Baltic Sea with the studied groundwaters, infiltrating microbes predominantly originated from deep soil groundwater. Most deep biosphere groundwater populations lacked surface representatives, suggesting that they have evolved from ancient autochthonous populations. We propose that deep biosphere groundwater communities in the Fennoscandian Shield consist of selected infiltrated and indigenous populations adapted to the prevailing conditions