Papers by Riikka Kietäväinen
Life
The deep bedrock surroundings are an analog for extraterrestrial habitats for life. In this study... more The deep bedrock surroundings are an analog for extraterrestrial habitats for life. In this study, we investigated microbial life within anoxic ultradeep boreholes in Precambrian bedrock, including the adaptation to environmental conditions and lifestyle of these organisms. Samples were collected from Pyhäsalmi mine environment in central Finland and from geothermal drilling wells in Otaniemi, Espoo, in southern Finland. Microbial communities inhabiting the up to 4.4 km deep bedrock were characterized with phylogenetic marker gene (16S rRNA genes and fungal ITS region) amplicon and DNA and cDNA metagenomic sequencing. Functional marker genes (dsrB, mcrA, narG) were quantified with qPCR. Results showed that although crystalline bedrock provides very limited substrates for life, the microbial communities are diverse. Gammaproteobacterial phylotypes were most dominant in both studied sites. Alkanindiges -affiliating OTU was dominating in Pyhäsalmi fluids, while different depths of Otan...
FEMS Microbiology Ecology
Deep, fresh groundwater in bedrock from Archaean eon hosts microbial community comprising of iron... more Deep, fresh groundwater in bedrock from Archaean eon hosts microbial community comprising of iron-oxidizing Gallionella, methanogenic and ammonia-oxidizing archaea in addition to diverse fungal communities.
Geosciences
The deep biosphere contains a large portion of the total microbial communities on Earth, but litt... more The deep biosphere contains a large portion of the total microbial communities on Earth, but little is known about the carbon sources that support deep life. In this study, we used Stable Isotope Probing (SIP) and high throughput amplicon sequencing to identify the acetate assimilating microbial communities at 2260 m depth in the bedrock of Outokumpu, Finland. The long-term and short-term effects of acetate on the microbial communities were assessed by DNA-targeted SIP and RNA targeted cell activation. The microbial communities reacted within hours to the amended acetate. Archaeal taxa representing the rare biosphere at 2260 m depth were identified and linked to the cycling of acetate, and were shown to have an impact on the functions and activity of the microbial communities in general through small key carbon compounds. The major archaeal lineages identified to assimilate acetate and metabolites derived from the labelled acetate were Methanosarcina spp., Methanococcus spp., Methan...
Geochimica et Cosmochimica Acta
Despite a geological history characterized by high temperature and pressure processes and organic... more Despite a geological history characterized by high temperature and pressure processes and organic carbon deprived crystalline bedrock, large amounts of hydrocarbons are found in deep groundwaters within Precambrian continental shields. In many sites, methane comprises more that 80% of the dissolved gas phase reaching concentrations of tens of mmol l-1. In this study, we used isotopic methods to study the carbon isotope systematics and sources of crustal methane within the Fennoscandian Shield. The main study sites were the Outokumpu Deep Drill Hole and the Pyhäsalmi mine in Finland, both of which allow groundwater sampling down to 2.5 km depth and have been previously studied for their groundwater chemistry and microbiology. We show that the differences in the amount and isotopic composition of methane are related to the availability of carbon sources as well as processes behind the incorporation of hydrogen and carbon via abiotic and biotic pathways into hydrocarbon molecules. Supported by previously reported occurrences and isotopic data of deep groundwater methane in lithologically different locations in Finland and Sweden, we show that methane formation is controlled by microbial methanogenesis and abiotic reactions, as well as lithology with the metasedimentary environments being the most favourable for methane occurrence. Rather than a thermogenic relic, crustal methane within the Fennoscandian Shield is more likely the result of low temperature formation from ancient organic compounds or their inorganic intermediates such as graphite. Such crustal gases are characterized by the lack of major amounts of C 2 + hydrocarbons and 13 C rich methane. Further, microbiological and isotopic geochemical evidence suggest that microbial methane is more common at depths shallower than 1.5 km.
Biogeosciences, 2016
The bacterial and archaeal community composition and the possible carbon assimilation processes a... more The bacterial and archaeal community composition and the possible carbon assimilation processes and energy sources of microbial communities in oligotrophic, deep, crystalline bedrock fractures is yet to be resolved. In this study, intrinsic microbial communities from groundwater of six fracture zones from 180 to 2300 m depths in Outokumpu bedrock were characterized using high-throughput amplicon sequencing and metagenomic prediction. <i>Comamonadaceae</i>-, <i>Anaerobrancaceae</i>- and <i>Pseudomonadaceae</i>-related operational taxonomic units (OTUs) form the core community in deep crystalline bedrock fractures in Outokumpu. Archaeal communities were mainly composed of <i>Methanobacteriaceae</i>-affiliating OTUs. The predicted bacterial metagenomes showed that pathways involved in fatty acid and amino sugar metabolism were common. In addition, relative abundance of genes coding the enzymes of autotrophic carbon fixation pathways in pr...
Frontiers in Microbiology, 2015
Pyhäsalmi mine in central Finland provides an excellent opportunity to study microbial and geoche... more Pyhäsalmi mine in central Finland provides an excellent opportunity to study microbial and geochemical processes in a deep subsurface crystalline rock environment through near-vertical drill holes that reach to a depth of more than two kilometers below the surface. However, microbial sampling was challenging in this high-pressure environment. Nucleic acid yields obtained were extremely low when compared to the cell counts detected (1.4 × 10 4 cells mL −1) in water. The water for nucleic acid analysis went through high decompression (60-130 bar) during sampling, whereas water samples for detection of cell counts by microscopy could be collected with slow decompression. No clear cells could be identified in water that went through high decompression. The high-pressure decompression may have damaged part of the cells and the nucleic acids escaped through the filter. The microbial diversity was analyzed from two drill holes by pyrosequencing amplicons of the bacterial and archaeal 16S rRNA genes and from the fungal ITS regions from both DNA and RNA fractions. The identified prokaryotic diversity was low, dominated by Firmicute, Beta-and Gammaproteobacteria species that are common in deep subsurface environments. The archaeal diversity consisted mainly of Methanobacteriales. Ascomycota dominated the fungal diversity and fungi were discovered to be active and to produce ribosomes in the deep oligotrophic biosphere. The deep fluids from the Pyhäsalmi mine shared several features with other deep Precambrian continental subsurface environments including saline, Ca-dominated water and stable isotope compositions positioning left from the meteoric water line. The dissolved gas phase was dominated by nitrogen but the gas composition clearly differed from that of atmospheric air. Despite carbon-poor conditions indicated by the lack of carbon-rich fracture fillings and only minor amounts of dissolved carbon detected in formation waters, some methane was found in the drill holes. No dramatic differences in gas compositions were observed between different gas sampling methods tested. For simple characterization of gas composition the most convenient way to collect samples is from free flowing fluid. However, compared to a pressurized method a relative decrease in the least soluble gases may appear.
Microorganisms
Fungi have an important role in nutrient cycling in most ecosystems on Earth, yet their ecology a... more Fungi have an important role in nutrient cycling in most ecosystems on Earth, yet their ecology and functionality in deep continental subsurface remain unknown. Here, we report the first observations of active fungal colonization of mica schist in the deep continental biosphere and the ability of deep subsurface fungi to attach to rock surfaces under in situ conditions in groundwater at 500 and 967 m depth in Precambrian bedrock. We present an in situ subsurface biofilm trap, designed to reveal sessile microbial communities on rock surface in deep continental groundwater, using Outokumpu Deep Drill Hole, in eastern Finland, as a test site. The observed fungal phyla in Outokumpu subsurface were Basidiomycota, Ascomycota, and Mortierellomycota. In addition, significant proportion of the community represented unclassified Fungi. Sessile fungal communities on mica schist surfaces differed from the planktic fungal communities. The main bacterial phyla were Firmicutes, Proteobacteria, and...
Microorganisms, 2015
Microorganisms in the deep biosphere are believed to conduct little metabolic activity due to low... more Microorganisms in the deep biosphere are believed to conduct little metabolic activity due to low nutrient availability in these environments. However, destructive penetration to long-isolated bedrock environments during construction of underground waste repositories can lead to increased nutrient availability and potentially affect the long-term stability of the repository systems, Here, we studied how microorganisms present in fracture fluid from a depth of 500 m in Outokumpu, Finland, respond to simple carbon compounds (C-1 compounds) in the presence or absence of sulphate as an electron acceptor. C-1 compounds such as methane and methanol are important intermediates in the deep subsurface carbon cycle, and electron acceptors such as sulphate are critical components of oxidation processes. Fracture fluid samples were incubated in vitro with either methane or methanol in the presence or absence of sulphate as an electron acceptor. Metabolic response was measured by staining the microbial cells with fluorescent dyes that indicate metabolic activity and transcriptional response with RT-qPCR. Our results show that deep subsurface microbes exist in dormant states but rapidly reactivate their transcription and respiration systems in the presence of C-1 substrates, particularly methane. Microbial activity was further enhanced by the addition of sulphate as an electron acceptor. Sulphate-and nitrate-reducing
Petrographic, geochemical, and geochronological data from shoshonitic lamprophyres from the North... more Petrographic, geochemical, and geochronological data from shoshonitic lamprophyres from the North Savo region, eastern Finland, and the NW Ladoga region, northwest Russia are presented. The two areas are found ~250 km apart along a roughly 450 km long palaeosuture between the Archaean Karelia Craton and the Proterozoic Svecofennian Domain. Two of the samples from North Savo are kersantites, while the remaining ten samples (from both North Savo and NW Ladoga) are minettes. Two morphologically different populations of zircon were identified from these lamprophyres and analysed by secondary ionisation mass spectrometry. Concordant analyses of inherited crustal zircon xenocrysts gave both Archaean and Proterozoic 207Pb/206Pb ages. In the NW Ladoga region, these are the first reported Archaean ages from south of the Meijeri Thrust zone. Large, homogeneous and relatively U- and Th-depleted zircons are interpreted as xenocrysts from the metasomatised mantle. U-(Th)-Pb analyses of these zircons resulted in ages of 1790 ± 3 Ma, 1784 ± 4 Ma, 1785 ± 5 Ma and 1781 ± 20 Ma, representative of the timing of dyke emplacement.
Geochemical characteristics of the dykes indicate that the source mantle experienced at least two types of metasomatic enrichment. The first of these was caused by a hydrous alkaline silicate melt, resulting in enrichment in SiO2, Al2O3, FeO, K2O, LILE and LREE. The second was caused by a carbonatitic melt that further enriched the source area in Ba, Th, U, Sr, P and LREE. Infiltration of melt along fractures in the mantle wedge probably resulted in a vein assemblage of biotite – (potassic) amphibole – apatite ± carbonate within unreacted mantle peridotite. The most likely source of the metasomatising melts was from partial melting of subducted carbonate-rich pelitic sediment.
FEMS Microbiology Ecology, 2013
Deep fracture zones in Finnish crystalline bedrock have been isolated for long, the oldest fluids... more Deep fracture zones in Finnish crystalline bedrock have been isolated for long, the oldest fluids being tens of millions of years old. To accurately measure the native microbial diversity in fracture-zone fluids, water samples were obtained by isolating the borehole fraction spanning a deep subsurface aquifer fracture zone with inflatable packers (500 and 967 m) or by pumping fluids directly from the fracture zone. Sampling frequency was examined to establish the time required for the space between packers to be flushed and replaced by indigenous fracture fluids. Chemical parameters of the fluid were monitored continuously, and samples were taken at three points during the flushing process. Microbial communities were characterized by comparison of 16S ribosomal genes and transcripts and quantification of dsrB (dissimilatory sulfate reduction) gene. Results suggest that fracture-zones host microbial communities with fewer cells and lower diversity than those in the drill hole prior to flushing. In addition, each fracture zone showed a community composition distinct from that inhabiting the drill hole at corresponding depth. The highest diversity was detected from the 967-m fracture zone. We conclude that the applied packer method can successfully isolate and sample authentic microbial fracture-zone communities of deep bedrock environments.
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Papers by Riikka Kietäväinen
Geochemical characteristics of the dykes indicate that the source mantle experienced at least two types of metasomatic enrichment. The first of these was caused by a hydrous alkaline silicate melt, resulting in enrichment in SiO2, Al2O3, FeO, K2O, LILE and LREE. The second was caused by a carbonatitic melt that further enriched the source area in Ba, Th, U, Sr, P and LREE. Infiltration of melt along fractures in the mantle wedge probably resulted in a vein assemblage of biotite – (potassic) amphibole – apatite ± carbonate within unreacted mantle peridotite. The most likely source of the metasomatising melts was from partial melting of subducted carbonate-rich pelitic sediment.
Geochemical characteristics of the dykes indicate that the source mantle experienced at least two types of metasomatic enrichment. The first of these was caused by a hydrous alkaline silicate melt, resulting in enrichment in SiO2, Al2O3, FeO, K2O, LILE and LREE. The second was caused by a carbonatitic melt that further enriched the source area in Ba, Th, U, Sr, P and LREE. Infiltration of melt along fractures in the mantle wedge probably resulted in a vein assemblage of biotite – (potassic) amphibole – apatite ± carbonate within unreacted mantle peridotite. The most likely source of the metasomatising melts was from partial melting of subducted carbonate-rich pelitic sediment.