Quantitation and Identification of Methanogens and Sulphate Reducers in Olkiluoto Groundwater

Malin Bomberg, Mari Nyyssönen, Merja Itävaara

    Research output: Book/ReportReport


    The GEOFUNC Project focuses on the microbiology connected to safety and risk
    assessment of the final disposal of high radioactive nuclear waste. Methanogenic
    archaea and sulphate reducing bacteria are significant groups of microorganisms in
    anaerobic environments, and are of crucial concern for the safe long term storage of
    nuclear waste in deep bedrock. The sulphate reducing bacteria are able to produce
    sulphide which may cause corrosion of the copper in the radioactive waste storage
    capsules. Methanogens, on the other hand, may produce quantities of methane from
    various organic carbon compounds, CO2 and H2. Methane may both serve as carbon
    source for methanotrophic microbial groups, and may also cause mobilization of
    radionuclides, as a result of gas discharge through fractures in the bedrock. The
    transition zones between the sulphate rich and methane rich waters are locations for
    microbial processes where the methane may serve as carbon source for sulphate
    reducing bacteria, which in turn would produce corrosive sulphides.

    It has been estimated that only 1-10 % of all the microorganisms present in the
    environment can be isolated and cultivated. Uncultured microorganisms can be
    identified and their numbers in the environment quantified by identification of specific
    marker genes that are essential for their functions by use of molecular methods.
    Methanogens, for example, can be identified by their genes for methyl coenzyme M
    reductase (mcrA), which is an essential enzyme involved in the production of methane.
    The mcrA is specifically present only in methanogenic archaea. Sulphate reducers are
    identified by their dissimilatory sulphite reductase genes (dsrB), which are present in
    and essential for all microorganisms performing dissimilatory sulphate reducing. In the
    GEOFUNC project, a quantitative PCR method (qPCR) was developed for the detection
    of methanogens and sulphate reducers. This method is based on specific quantitative
    detection of marker genes involved in methanogenesis (mcrA) or sulphate reduction
    (dsrB) and enables the study of these microbial processes in the deep bedrock

    In the GEOFUNC project, groundwater samples were studied from depths ranging from
    -14.5 m to -581 m comprising samples from both drillholes in Olkiluoto and
    groundwater stations in the ONKALO. Methanogenic archaea were present in almost all
    samples. The highest number of methanogens was detected in the samples ONK-PVA1
    (-14.5 m), OL-KR40 (-349 to -351 m and -545 to -553 m) and OL-KR47 (-334 to -338
    m) and OL-KR23 (-347 to -376 m). In the samples, where the salinity exceeded 19 g/l
    (Cl, Na, Ca), the number of methanogens was very low. Sulphate reducing bacteria
    were present in all studied samples. The highest number of sulphate reducers were
    detected in the samples ONK-PVA1 (-14.5 m), OL-KR23 (-347 to -376 m) and OLKR11 (-531 to -558 m) and OL-KR40 (-545 to -553 m), however, the last two samples are evident artefact mixtures of SO4- and CH4-rich groundwaters, thus they do not represent undisturbed in situ conditions in groundwater system.

    The diversity of methanogens changed in relation to depth and a clear division into
    phylogenetic groups containing either mcrA sequences from samples close to the land
    surface or mcrA sequences from deeper samples. The sulphate reducers were different
    in all studied samples. Despite their important ecological functions, both methanogens
    and sulphate reducers were present as only small fractions of the total microbial
    community in the Olkiluoto groundwater. The methanogens comprised at the most
    0.44 % of the microbial community (-349 m) and the sulphate reducers 1.55 % (-14.5
    m) and 1.3 % (-531 m).

    The results presented in this report give indications to the diversity and quantity of the
    populations of methanogenic archaea and sulphate reducing bacteria in the deep
    groundwater of Olkiluoto. In spite of the small number of methanogens and sulphate
    reducers in the environment there eological role is significant.
    Original languageEnglish
    Place of PublicationOlkiluoto
    Number of pages56
    Publication statusPublished - 2010
    MoE publication typeD4 Published development or research report or study

    Publication series

    SeriesPosiva Working Report


    • archaea
    • methanogen
    • methane
    • sulphate reducing bacteria SRB
    • sulphate
    • quantitative PCR
    • phylogenetic analysis
    • microbial community composition
    • deep groundwater


    Dive into the research topics of 'Quantitation and Identification of Methanogens and Sulphate Reducers in Olkiluoto Groundwater'. Together they form a unique fingerprint.

    Cite this