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The groundwater system in Olkiluoto, Finland, is stratified with a mixing layer at a depth of approximately 300 m between sulphate-rich, methane-poor and sulphate-poor, methane-rich groundwaters. New sequence library data obtained by 454 pyrotag sequencing of the v4v6 16S rDNA region indicated that sulphate-reducing bacteria (SRB) dominated the mixing layer while SRB could not be detected in the deep sulphate-poor groundwater samples. With the indispensable support of the sequence data, it could be demonstrated that sulphate was the only component needed to trigger a very large community transition in deep sulphate-poor, methane-rich groundwater from a non-sulphate-reducing community comprisingHydrogenophaga,Pseudomonas,Thiobacillus,Fusibacter, andLutibacterto a sulphate-reducing community withDesulfobacula,Desulfovibrio,Desufobulbaceae,Desulfobacterium,Desulfosporosinus, andDesulfotignum. Experiments with biofilms and planktonic microorganisms in flow cells underin situconditions confirmed that adding sulphate to the sulphate-poor groundwater generated growth of cultivable SRB and detectable SRB-related sequences. It was also found that the 16S rDNA diversity of the biofilms was conserved over 103 d and that there was great similarity in diversity between the microorganisms in the biofilms and in the flowing groundwater. This work demonstrates that the presence/absence of only one geochemical parameter, i.e., sulphate, in the groundwater significantly influenced the diversity of the investigated subterranean microbial community. [ABSTRACT FROM PUBLISHER]

Sediments in the Indian Ocean off the coast of the Indonesian island Sumatra were sampled at 25 stations in high resolution near the sediment surface and at three stations up to a maximum depth of 12 meter below seafloor (mbsf) for a quantitative microbial community analysis. Total cell counts were determined applying two different protocols including SYBR Green II as fluorescent staining dye. Total cell counts without detaching cells from sediment particles were 109 cells/ mL sediments at the sediment surface with little variation between all stations. They decreased to 108 cells/ mL at 0.2 to 0.4 mbsf and to 107 cells/ mL below 6 mbsf. The total cell counts after detaching cells from sediment particles were up to one order of magnitude lower above 6 mbsf and showed similar values below. This difference for the two protocols can be explained by a loss of cells during the detachment procedure and/or counting of unspecific signals without detaching cells from sediment particles. Particular phylogenetic and physiological prokaryotic groups were quantified by quantitative, real-time PCR (Q-PCR) targeting 16S rRNA and functional genes. Archaea and Bacteria were found overall in similar 16S rRNA gene copy numbers in the range of the total cell counts at all sediment depths, thus, neither Archaea nor Bacteria could be considered as dominant. The eukaryotic 18S rRNA gene occurred in two orders of magnitude lower numbers than prokaryotic 16S rRNA genes. Fe(III)- and Mn(IV)-reducing bacteria (16S rRNA gene of Geobacteraceae) and sulfate-reducing bacteria (functional gene dsrA) were detected in variable (up to 108 gene copies/ mL sediment) but in always significantly lower numbers than total Bacteria. The proportion of sulfate reducers on the prokaryotic community was between 0.2 and 19%. Calculated aereal sulfate reduction rates were overall low with values between 0.002 and 0.027 mmol m- 2a- 1, resulting in sulfate reduction rates per cell of 0.0007 and 0.81 fmol cell- 1 a- 1, similar to published data for other deeply buried marine sediments. Methanogenesis did not seem to play a big role since methane was detected only below 6.5 mbsf, and the functional gene of methanogens and anaerobic methanotrophs mcrA could not be detected in any sample. [ABSTRACT FROM AUTHOR]

In deep subsurface sediments of the Juan de Fuca Ridge Flank, porewater acetate that is depleted in 13C relative to sedimentary organic matter indicates an acetogenic component to total acetate production. Thermodynamic calculations indicate common fermentation products or lignin monomers as potential substrates for acetogenesis. The classic autotrophic reaction may contribute as well, provided that dihydrogen (H2) concentrations are not drawn down to the thermodynamic thresholds of the energetically more favorable processes of sulfate reduction and methanogenesis. A high diversity of novel formyl tetrahydrofolate synthetase (fhs) genes throughout the upper half of the sediment column indicates the genetic potential for acetogenesis. Our results suggest that a substantial fraction of the acetate produced in marine sediment porewaters may derive from acetogenesis, in addition to the conventionally invoked sources fermentation and sulfate reduction. [ABSTRACT FROM AUTHOR]

The importance of crustal fluid chemical composition in driving the marine deep subseafloor biosphere was examined in northeast Pacific ridge-flank sediments. At IODP Site U1301, sulfate from crustal fluids diffuses into overlying sediments, forming a transition zone where sulfate meets in situ-produced methane. Enhanced cell counts and metabolic activity suggest that sulfate stimulates microbial respiration, specifically anaerobic methane oxidation coupled to sulfate reduction. Cell counts and activity are also elevated in basement-near layers. Owing to the worldwide expansion of the crustal aquifer, we postulate that crustal fluids may fuel the marine deep subseafloor biosphere on a global scale. [ABSTRACT FROM AUTHOR]