Microbiology, chemistry and dissolved gas in groundwater from Olkiluoto, Finland, were analysed over 3 years; samples came from 16 shallow observation tubes and boreholes from depths of 3.9-16.2 m and 14 deep boreholes from depths of 35-742 m. The average total number of cells (TNC) was 3.9 Â 10 5 cells per ml in the shallow groundwater and 5.7 Â 10 4 cells per ml in the deep groundwater. There was a significant correlation between the amount of biomass, analysed as ATP concentration, and TNC. ATP concentration also correlated with the stacked output of anaerobic most probable number cultivations of nitrate-, iron-, manganese-and sulphate-reducing bacteria, and acetogenic bacteria and methanogens. The numbers and biomass varied at most by approximately three orders of magnitude between boreholes, and TNC and ATP were positively related to the concentration of dissolved organic carbon. Two depth zones were found where the numbers, biomass and diversity of the microbial populations peaked. Shallow groundwater down to a depth of 16.2 m on average contained more biomass and cultivable microorganisms than did deep groundwater, except in a zone at a depth of approximately 300 m where the average biomass and number of cultivable microorganisms approached those of shallow groundwater. Starting at a depth of approximately 300 m, there were steep gradients of decreasing sulphate and increasing methane concentrations with depth; together with the peaks in biomass and sulphide concentration at this depth, these suggest that anaerobic methane oxidation may be a significant process at depth in Olkiluoto.

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This paper describes how groundwater was sampled, DNA extracted, amplified and cloned and how information available in the ribosomal 16S rRNA gene was used for mapping diversity and distribution of subterranean bacteria in groundwater at the Bangombé site in the Oklo region. The results showed that this site was inhabited by a diversified population of bacteria. Each borehole was dominated by species that did not dominate in any of the other boreholes; a result that probably reflects documented differences in the geochemical environment. Two of the sequences obtained were identified at genus level to represent Acinetobacter and Zoogloea, but most of the 44 sequences found were only distantly related to species in the DNA database. The deepest borehole, BAX01 (105 m), had the highest number of bacteria and also total organic carbon (TOC). This borehole harboured only Proteobacteria beta group sequences while sequences related to Proteobacteria beta, gamma and delta groups and Gram‐positive bacteria were found in the other four boreholes. Two of the boreholes, BAX02 (34 m) and BAX04 (10 m) had many 16S rRNA gene sequences in common and they also had similar counts of bacteria, content of TOC, pH and equal conductivity, suggesting a hydraulic connection between them.

This paper presents the molecular characterization of attached bacterial populations growing in slowly flowing artesian groundwater from deep crystalline bed-rock of the Stripa mine, south central Sweden. Bacteria grew on 90 Gotebor;, Swede-n glass slides in laminar flow reactors connected to the anoxic groundwater flowing up through tubing from two levels of a borehole, 812-820 m and 970-1240 m. The glass slides were collected, the bacterial DNA was extracted and the 165 rRNA genes were amplified by PCR using primers matching universally conserved positions 51 9-536 and 1392-1405. The resulting PCR fragments were subsequently cloned and sequenced. The sequences were compared with each other and with 165 rRNA gene sequences in the EMBL database. Three major groups of bacteria were found. Signature bases placed the clones in the appropriate systematic groups. All belonged to the proteobacterial groups beta and gamma. One group was found only a t the 812-820 m level, where it constituted 63% of the sequenced clones, whereas the second group existed almost exclusively a t the 970-1240 m level, where it constituted 83% of the sequenced clones. The third group was equally distributed between the levels. A f e w other bacteria were also found. None of the 165 rRNA genes from the dominant bacteria showed more than 88% similarity to any of the others, and none of them resembled anything in the database by more than 96%. Temperature did not seem to have any effect on species composition a t the deeper level. SEM images showed rods appearing in microcolonies. The conditions a t the levels differ in pH, temperature, redox and flow rate, and in content of sulphate, iron and sulphide. The presence of one dominant species in the laminar-flow reactors a t each level indicates that the environments might have offered restrictive physical or physiological conditions difficult to adapt to.