Microbial populations in 16 groundwater samples from six Fennoscandian Shield sites in Finland and Sweden were investigated. The average total cell number was 3.7×10
5 cells ml
−1, and there was no ...change in the mean of the total cell numbers to a depth of 1390 m. Culture media were designed based on the chemical composition of each groundwater sample and used successfully to culture anaerobic microorganisms from all samples between 65 and 1350 m depth. Between 0.0084 and 14.8% of total cells were cultured from groundwater samples. Sulfate-reducing bacteria, iron-reducing bacteria and heterotrophic acetogenic bacteria were cultured from groundwater sampled at 65–686 m depth in geographically distant sites. Different microbial populations were cultured from deeper, older and more saline groundwater from 863 to 1350 m depth. Principal component analysis of groundwater chemistry data showed that sulfate- and iron-reducing bacteria were not detected in the most saline groundwater. Iron-reducing bacteria and acetogens were cultured from deep groundwater that contained 0.35–3.5 mM sulfate, while methanogens and acetogens were cultured from deep sulfate-depleted groundwater. In one borehole from which autotrophic methanogens were cultured, dissolved inorganic carbon was enriched in
13C compared to other Fennoscandian Shield groundwater samples, suggesting that autotrophs were active. It can be concluded that a diverse microbial community is present from the surface to over 1300 m depth in the Fennoscandian Shield.
Groundwater samples from 200- to 950-m depths in four igneous rock sites in Finland were investigated for different metabolic groups of microorganisms, and the data were compared with the available ...geochemical record. Samples were collected with a pressurized groundwater sampling system developed for gas and microbiological sampling. Two of the sites had groundwater that was fresh, with < 0.2 g/l dissolved solids, whereas that at the two other sites was much more saline, reaching a maximum of 24 g/l dissolved solids. The groundwater contained gases, 33 to 340 ml/l, with nitrogen or methane dominating. Total cell numbers were 10 5 to 10 6 cells/ml, which is typical for deep igneous rock aquifers. Growth media were designed to mimic the actual groundwater chemistry at each sampling point and used for most probable number enumeration of methanogens, acetogens, sulfate-reducing bacteria (SRB), and iron-reducing bacteria (IRB). SRB predominated in sites where iron sulfide fracture-filling minerals are common. IRB were the main population in one site where iron sulfide fracture minerals are not present, but iron hydroxide fracture minerals predominate. Fracture-filling minerals were a better indicator of microbial populations than was groundwater chemistry. Low numbers of autotrophic methanogens were cultured. One of several possible interpretations of stable isotope data suggested that most of the detected methane is thermogenic, which would correlate with few active methanogens. However, we concluded other interpretations were also possible.
Desulfovibrio vulgaris Hildenborough is a model organism for studying the energy metabolism of sulfate-reducing bacteria (SRB) and for understanding the economic impacts of SRB, including ...biocorrosion of metal infrastructure and bioremediation of toxic metal ions. The 3,570,858 base pair (bp) genome sequence reveals a network of novel c-type cytochromes, connecting multiple periplasmic hydrogenases and formate dehydrogenases, as a key feature of its energy metabolism. The relative arrangement of genes encoding enzymes for energy transduction, together with inferred cellular location of the enzymes, provides a basis for proposing an expansion to the 'hydrogen-cycling' model for increasing energy efficiency in this bacterium. Plasmid-encoded functions include modification of cell surface components, nitrogen fixation and a type-III protein secretion system. This genome sequence represents a substantial step toward the elucidation of pathways for reduction (and bioremediation) of pollutants such as uranium and chromium and offers a new starting point for defining this organism's complex anaerobic respiration.
Progress in studying the active biosphere in the deep seafloor is currently limited by the unknown amount of drilling-induced microbial contamination. Contamination tests were conducted during Leg ...185 of the Ocean Drilling Program on the drillship JOIDES Resolution to assess the suitability of this platform for deep biosphere research. Tests using both a chemical tracer perfluoro(methylcyclohexane) and a particulate tracer (0.5- mu m-diameter fluorescent microspheres) were conducted during coring with the advanced hydraulic piston core in unconsolidated sediments and with the rotary core barrel and diamond core barrel in igneous rock. Detection of both types of tracers on the exterior of recovered cores confirmed successful delivery. The particulate tracer was never detected in the interior of unconsolidated sediment (n = 24). The average concentration of the chemical tracer (n = 12) was equivalent to 0.35 mu L of drilling fluid per gram of sediment. The particulate tracer was not found in the interiors of igneous rock samples that were crushed (n = 4) but was found in the interiors of 64% of the thin sections examined (n = 12), indicating that the samples were contaminated during sectioning rather than drilling. Perfluorocarbon data indicate that drilling fluid in the igneous rock samples averaged 0.01 mu L g super(-1) rock. Based on the abundance of bacteria in the surface seawater (4.2 10 super(8)L super(-1)), which was used as the drilling fluid, the potential contamination of both sample types is on the order of a few bacteria per gram of cored material. This estimate is conservative, given the high pervasiveness of the perfluorocarbon tracer relative to microbes.
Natural analogues allow scientists to investigate biogeochemical processes relevant to radioactive waste disposal that occur on time scales longer than those that may be studied by time-limited ...laboratory experiments. The Palmottu U–Th deposit in Finland and the Bangombé natural nuclear reactor in Gabon involve the study of natural uranium, and are both considered natural analogues for subsurface radioactive waste disposal. The microbial population naturally present in groundwater may affect the redox conditions, and hence, the radionuclide solubility and migration. Therefore, groundwater samples from the two sites were investigated for microbial populations. The total numbers of cells ranged from 10
4 to 10
6 cells ml
−1. Iron-reducing bacteria (IRB) were the largest culturable microbial population in the Palmottu groundwater and were present at up to 1.3×10
5 cells ml
−1. Sulfate-reducing bacteria (SRB) and acetogens could also be cultured from the Palmottu groundwater. The numbers of IRB and SRB were largest in groundwater with the lowest uranium concentrations. Removal of dissolved U(VI) from solution was concomitant with the growth of IRB enrichment cultures and the reduction of iron. The redox buffer in the Palmottu groundwater consists of iron and uranium species, both of which are affected by IRB. IRB and aerobic heterotrophs were cultured from the Bangombé groundwater, where redox potentials are buffered by iron and organic carbon species. Microbial populations similar to those found at Palmottu and Bangombé are found throughout the Fennoscandian Shield, a potential host rock for subsurface radioactive waste disposal. These results confirm that microorganisms can be expected to play a role in stabilizing radioactive waste disposed of in the subsurface by lowering redox potential and immobilizing radionuclides.
A full-scale nuclear fuel waste disposal container experiment was carried out 240 m below ground in an underground granitic rock research laboratory in Canada. An electric heater was surrounded by ...buffer material composed of sand and bentonite clay and provided heat equivalent to what is anticipated in a Canadian nuclear fuel waste repository. During the experiment, the heat caused a mass transport of water and moisture content gradients developed in the buffer ranging from 13% closest to the heater to 23% at the rock wall of the deposition hole. Upon decommissioning after 2.5 years, microorganisms could be cultured from all samples having a moisture content above 15% but not from samples with a moisture content below 15%. Heterotrophic aerobic and anaerobic bacteria were found in numbers ranging from 10(1) to 10(6) cells/g dry weight buffer. Approximately 10(2), or less, sulphate-reducing bacteria and methanogens per gram of dry weight buffer were also found. Identification of buffer population members was performed using Analytical Profile Index (API) strips for isolated bacteria and 16S rRNA gene sequencing for in situ samples. A total of 79 isolates from five buffer layers were identified with API strips as representing the beta, gamma and delta groups of Proteobacteria and Gram-positive bacteria. Sixty-seven 16S rRNA clones that were obtained from three buffer layers were classified into 21 clone groups representing alpha and gamma groups of Proteobacteria, Gram-positive bacteria, and a yeast. Approximately 20% of the population comprised Gram-positive bacteria. Members of the genera Amycolatopsis, Bacillus, and Nocardia predominated. Among Gram-negative bacteria, the genera Acinetobacter and Pseudomonas predominated. Analysis of lipid biomarker signatures and in situ leucine uptake demonstrated that the buffer population was viable. The results suggest that a nuclear fuel waste buffer will be populated by active microorganisms only if the moisture content is above a value where free water is available for active life.
The City of Fredericton, New Brunswick, Canada obtains its water from the Saint John River-recharged Fredericton aquifer. Water quality improves as it flows from the river into the aquifer in a ...process called bank filtration. Microorganisms contribute to water quality improvements during bank filtration by removing organic carbon. In the Fredericton aquifer, microbially catalyzed reductive dissolution of manganese oxide minerals negatively affects water quality. Aerobic and anaerobic microorganisms were cultured from Fredericton aquifer production well water, from associated bedrock groundwater, and from Saint John River sediment core and sediment groundwater samples. Aerobes were the largest culturable groups in all samples. The ratio of aerobes to other microbial groups, i.e., those reducing nitrate, Mn
4 +
, Fe
3 +
, or sulfate, did not vary significantly along the water flow path from the river to the aquifer. Analysis of microbial community composition along the flow path indicated an essentially identical community except in the immediate vicinity of the aquifer. This is in agreement with the absence of macroscale redox zones in the sediment below the Saint John River as determined by groundwater geochemical data. Bacteria isolated from groundwater samples, identified by 16S ribosomal RNA gene sequencing, were α -, β -, γ -, and δ -Proteobacteria, Actinobacteria, and Firmicutes. In contrast to groundwater samples, the majority of bacteria isolated from sediments were γ -Proteobacteria. Numbers of manganese-reducing bacteria, including Aeromonas spp., were small, however Mn
4 +
reduction ability was widespread in bacteria enriched and isolated with other electron acceptors. The diverse Fredericton aquifer microbial community likely uses manganese oxide minerals as a sink for electrons derived from organic carbon oxidation.
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