Distribution, diversity, and activity of sulfate-reducing bacteria in the water column in Gek-Gel Lake, Azerbaijan

The distribution and activity of sulfate-reducing bacteria (SRB) in the water column of the alpine meromictic Gek-Gel lake were studied. Apart from traditional microbiological methods based on cultivation and on measuring the process rates with radioactive labels, in situ fluorescent hybridization (FISH) was used, which enables identification and quantification without cultivating organisms. The peak rate of sulfate reduction, 0.486 microg S/(l day), was found in the chemocline at 33 m. The peak SRB number of 2.5 x 106 cells/ml, as determined by the end-point dilutions method on selective media, was found at the same depth. The phylogenetic position of the SRB, as determined by FISH, revealed the predominance of the Desulfovibrio spp., Desulfobulbus spp., and Desulfoarculus spp./Desulfomonile spp. groups. The numbers of spore-forming Desulfotomaculum spp. increased with depth. The low measured rates of sulfate reduction accompanied with high SRB numbers and the predominance of the groups capable of reducing a wide range of substrates permit us to propose utilization of electron acceptors other than sulfate as the main activity of the SRB in the water column.     

Community Structure, Cellular rRNA Content, and Activity of Sulfate-Reducing Bacteria in Marine Arctic Sediments

The community structure of sulfate-reducing bacteria (SRB) of a marine Arctic sediment (Smeerenburgfjorden, Svalbard) was characterized by both fluorescence in situ hybridization (FISH) and rRNA slot blot hybridization by using group- and genus-specific 16S rRNA-targeted oligonucleotide probes. The SRB community was dominated by members of the Desulfosarcina-Desulfococcus group. This group accounted for up to 73% of the SRB detected and up to 70% of the SRB rRNA detected. The predominance was shown to be a common feature for different stations along the coast of Svalbard. In a top-to-bottom approach we aimed to further resolve the composition of this large group of SRB by using probes for cultivated genera. While this approach failed, directed cloning of probe-targeted genes encoding 16S rRNA was successful and resulted in sequences which were all affiliated with the Desulfosarcina-Desulfococcus group. A group of clone sequences (group SVAL1) most closely related to Desulfosarcina variabilis (91.2% sequence similarity) was dominant and was shown to be most abundant in situ, accounting for up to 54.8% of the total SRB detected. A comparison of the two methods used for quantification showed that FISH and rRNA slot blot hybridization gave comparable results. Furthermore, a combination of the two methods allowed us to calculate specific cellular rRNA contents with respect to localization in the sediment profile. The rRNA contents of Desulfosarcina-Desulfococcus cells were highest in the first 5 mm of the sediment (0.9 and 1.4 fg, respectively) and decreased steeply with depth, indicating that maximal metabolic activity occurred close to the surface. Based on SRB cell numbers, cellular sulfate reduction rates were calculated. The rates were highest in the surface layer (0.14 fmol cell⁻¹ day⁻¹), decreased by a factor of 3 within the first 2 cm, and were relatively constant in deeper layers.     

Sulfate reduction and methanogenesis in the Shira and Shunet meromictic lakes (Khakasia, Russia)

The biogeochemical and molecular biological study of the chemocline and sediments of saline meromictic lakes Shira and Shunet (Khakasia, Russia) was performed. A marked increase in the rates of sulfate reduction and methanogenesis was revealed at the medium depths of the chemocline. The rates of these processes in the bottom sediments decreased with depth. The numbers of the members of domains Bacteria, Archaea, and of sulfate-reducing bacteria (SRB) were determined by fluorescence in situ hybridization with rRNA specific oligonucleotide probes labeled with horseradish peroxidase and subsequent tyramide signal amplification. In the chemocline, both the total microbial numbers and those of Bacteria were shown to increase with depth. The archaea and SRB were present in almost equal numbers. In the lake sediments, a drastic decrease in microbial numbers with depth was revealed. SRB were found to prevail in the upper sediment layer and archaea in the lower one. This finding correlated with the measured rates of sulfate reduction and methanogenesis.     

Indicators of Microbial Sulfate Reduction in Acidic Sulfide-Rich Mine Tailings

Sulfate-reducing bacteria (SRB) are thought to be actively involved in the cycling of sulfur in acidic mine tailings. However, most studies have used circumstantial evidence to assess microbial sulfate activity in such environments. In order to fully ascertain the role of sulfate-reducing bacteria (SRB) in sulfur cycling in acidic mine tailings, we measured sulfate reduction rates, sulfur isotopic composition of reduced sulfide fractions, porewaters and solid-phase geochemistry and SRB populations in four different Cu-Zn tailings located in Timmins, Ontario, Canada. The tailings were sampled in the summer and in the spring, shortly after snowmelt. The results first indicate that all four sites showed very high sulfate reduction rates in the summer (～100–1000 nmol cm^{? 3}d^?1), which corresponded to the presence of sulfide in the porewaters and to high SRB populations. In some of the sites, zones of microbial sulfate reduction also corresponded to a decline of organic carbon and to an apparent pyrite (with slightly negative δ³⁴S values) enrichment around the same depth. Microbial sulfate reduction was also important in permanently acidic (pH 2–3) mine tailings sites, suggesting that SRB can be active under very acidic conditions. Secondly, the results showed that microbial sulfate reduction was greatly reduced in the spring, suggesting that temperature might be a key factor in the activity of SRB. However, a closer look at the results indicated that temperature was not the sole factor and that acidic conditions and limited substrate availability in the spring appeared to be important as well in limiting microbial sulfate par reduction in sulfidic mine tailings. Finally, the results indicate that sulfur undergoes rapid cycling throughout the year and that microbial sulfate reduction and metal sulfide precipitation do not appear to be a permanent sink for metals.     

Community structure, cellular rRNA content, and activity of sulfate-reducing bacteria in marine arctic sediments

The community structure of sulfate-reducing bacteria (SRB) of a marine Arctic sediment (Smeerenburgfjorden, Svalbard) was characterized by both fluorescence in situ hybridization (FISH) and rRNA slot blot hybridization by using group- and genus-specific 16S rRNA-targeted oligonucleotide probes. The SRB community was dominated by members of the Desulfosarcina-Desulfococcus group. This group accounted for up to 73% of the SRB detected and up to 70% of the SRB rRNA detected. The predominance was shown to be a common feature for different stations along the coast of Svalbard. In a top-to-bottom approach we aimed to further resolve the composition of this large group of SRB by using probes for cultivated genera. While this approach failed, directed cloning of probe-targeted genes encoding 16S rRNA was successful and resulted in sequences which were all affiliated with the Desulfosarcina-Desulfococcus group. A group of clone sequences (group SVAL1) most closely related to Desulfosarcina variabilis (91.2% sequence similarity) was dominant and was shown to be most abundant in situ, accounting for up to 54. 8% of the total SRB detected. A comparison of the two methods used for quantification showed that FISH and rRNA slot blot hybridization gave comparable results. Furthermore, a combination of the two methods allowed us to calculate specific cellular rRNA contents with respect to localization in the sediment profile. The rRNA contents of Desulfosarcina-Desulfococcus cells were highest in the first 5 mm of the sediment (0.9 and 1.4 fg, respectively) and decreased steeply with depth, indicating that maximal metabolic activity occurred close to the surface. Based on SRB cell numbers, cellular sulfate reduction rates were calculated. The rates were highest in the surface layer (0.14 fmol cell(-1) day(-1)), decreased by a factor of 3 within the first 2 cm, and were relatively constant in deeper layers.     

Activity and Diversity of Sulfate-Reducing Bacteria in a Petroleum Hydrocarbon-Contaminated Aquifer

Microbial sulfate reduction is an important metabolic activity in petroleum hydrocarbon (PHC)-contaminated aquifers. We quantified carbon source-enhanced microbial SO₄²⁻ reduction in a PHC-contaminated aquifer by using single-well push-pull tests and related the consumption of sulfate and added carbon sources to the presence of certain genera of sulfate-reducing bacteria (SRB). We also used molecular methods to assess suspended SRB diversity. In four consecutive tests, we injected anoxic test solutions (1,000 liters) containing bromide as a conservative tracer, sulfate, and either propionate, butyrate, lactate, or acetate as reactants into an existing monitoring well. After an initial incubation period, 1,000 liters of test solution-groundwater mixture was extracted from the same well. Average total test duration was 71 h. We measured concentrations of bromide, sulfate, and carbon sources in native groundwater as well as in injection and extraction phase samples and characterized the SRB population by using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE). Enhanced sulfate reduction concomitant with carbon source degradation was observed in all tests. Computed first-order rate coefficients ranged from 0.19 to 0.32 day⁻¹ for sulfate reduction and from 0.13 to 0.60 day⁻¹ for carbon source degradation. Sulfur isotope fractionation in unconsumed sulfate indicated that sulfate reduction was microbially mediated. Enhancement of sulfate reduction due to carbon source additions in all tests and variability of rate coefficients suggested the presence of specific SRB genera and a high diversity of SRB. We confirmed this by using FISH and DGGE. A large fraction of suspended bacteria hybridized with SRB-targeting probes SRB385 plus SRB385-Db (11 to 24% of total cells). FISH results showed that the activity of these bacteria was enhanced by addition of sulfate and carbon sources during push-pull tests. However, DGGE profiles indicated that the bacterial community structure of the dominant species did not change during the tests. Thus, the combination of push-pull tests with molecular methods provided valuable insights into microbial processes, activities, and diversity in the sulfate-reducing zone of a PHC-contaminated aquifer.     

Microbial processes of the carbon and sulfur cycles in the White Sea

The present paper contains the results of our microbiological and biogeochemical investigations carried out during a series of expeditions to the White Sea in 2002–2006. The studies were conducted in the open part of the White Sea, as well as in the Onega, Dvina, and Kandalaksha bays. In August 2006, the photosynthetic productivity in the surface water layer was low (47–145 mg C m^?2 day^?1). Quantitative characteristics of microbial numbers and activity of the the key microbial processes occurring in the water column of the White Sea were explored. Over the 5-year period of observations, the total number of bacterial cells in the surface layer of the water column varied from 50 to 600 thousand cells ml^?1. In August 2006, bacterioplankton production (BP) was estimated to be 0.26–3.3 μg C l^?1 day^?1; the P/B coefficient varied from 0.22 to 0.93. The suspended organic matter had a lighter isotope composition (from ?28.0 to ?30.5‰) due to the predominance of terrigenous organic matter delivered by the Northern Dvina waters. The interseasonal and interannual variation coefficients for phytoplankton production and BP numbers are compared. The bacterioplankton community of the White Sea’s deep water was found to be more stable than that of the surface layer. In the surface layer of bottom sediments, methane concentration was 0.2–5.2 μl dm^?3; the rate of bacterial sulfate reduction was 18–260 μg S dm^?3 day^?1; and the rates of methane production and oxidation were 24–123 and 6–13 nl CH₄ dm^?3 day^?1, respectively. We demonstrated that the rates of microbial processes of the carbon and sulfur cycles occurring in the sediments of the White Sea basin were low.     

Major substrates for microbial sulfate reduction in the sediments of Ise Bay, Japan

To clarify the anaerobic microbial interactions in the process of carbon mineralization in marine eutrophic environments, the microbial sulfate reduction and methane production rates were examined in coastal marine sediments of Ise Bay, Japan, in autumn 1990. Sulfate reduction rates (51–210 nmol ml⁻¹ day⁻¹ at 24°C) were much higher than the methane production ones (<1.78 nmol ml⁻¹ day⁻¹) in the surface sediments (top 2 cm) at the six stations surveyed (water depth: 10.7–23.3 m). Substrates for sulfate-reducing bacteria (SRB) were estimated after the addition of a specific inhibitor for SRB (20 mmol l⁻¹ molybdate) into the sediment slurry, from the substrate accumulation rates. In the presence of the inhibitor, sulfate reduction was completely stopped and volatile fatty acids (mainly acetate) were accumulated, although hydrogen was not. Methane production occurred markedly accompanied by consumption of the accumulated acetate from the third day after the addition of molybdate. The maximum rate of methane production was 1.2–1.9 μmol ml⁻¹ day⁻¹, which was similar to those in highly polluted freshwater sediments such as the Tama River, Tokyo, Japan. These results show that acetate is a common major substrate for sulfate reduction and methane production, and SRB competitively inhibit potential acetoclastic methanogenesis in coastal sediments. Methanogens may potentially inhabit the sediments at low levels of population density and activity.     

Diversity, Activity, and Abundance of Sulfate-Reducing Bacteria in Saline and Hypersaline Soda Lakes

Soda lakes are naturally occurring highly alkaline and saline environments. Although the sulfur cycle is one of the most active element cycles in these lakes, little is known about the sulfate-reducing bacteria (SRB). In this study we investigated the diversity, activity, and abundance of SRB in sediment samples and enrichment cultures from a range of (hyper)saline soda lakes of the Kulunda Steppe in southeastern Siberia in Russia. For this purpose, a polyphasic approach was used, including denaturing gradient gel electrophoresis of dsr gene fragments, sulfate reduction rate measurements, serial dilutions, and quantitative real-time PCR (qPCR). Comparative sequence analysis revealed the presence of several novel clusters of SRB, mostly affiliated with members of the order Desulfovibrionales and family Desulfobacteraceae. We detected sulfate reducers and observed substantial sulfate reducing rates (between 12 and 423 μmol/dm³ day⁻¹) for most lakes, even at a salinity of 475 g/liter. Enrichments were obtained at salt saturating conditions (4 M Na⁺), using H₂ or volatile fatty acids as electron donors, and an extremely halophilic SRB, strain ASO3-1, was isolated. Furthermore, a high dsr gene copy number of 10⁸ cells per ml was detected in a hypersaline lake by qPCR. Our results indicate the presence of diverse and active SRB communities in these extreme ecosystems.     

Sulfonates as Terminal Electron Acceptors for Growth of Sulfite-Reducing Bacteria (Desulfitobacterium spp.) and Sulfate-Reducing Bacteria: Effects of Inhibitors of Sulfidogenesis

This study demonstrates the ability of Desulfitobacterium spp. to utilize aliphatic sulfonates as terminal electron acceptors (TEA) for growth. Isethionate (2-hydroxyethanesulfonate) reduction by Desulfitobacterium hafniense resulted in acetate as well as sulfide accumulation in accordance with the expectation that the carbon portion of isethionate was oxidized to acetate and the sulfur was reduced to sulfide. The presence of a polypeptide, approximately 97 kDa, was evident in isethionate-grown cells of Desulfitobacterium hafniense, Desulfitobacterium sp. strain PCE 1, and the two sulfate-reducing bacteria (SRB)—Desulfovibrio desulfuricans IC1 (T. J. Lie, J. R. Leadbetter, and E. R. Leadbetter, Geomicrobiol. J. 15:135–149, 1998) and Desulfomicrobium norvegicum; this polypeptide was not detected when these bacteria were grown on TEA other than isethionate, suggesting involvement in its metabolism. The sulfate analogs molybdate and tungstate, effective in inhibiting sulfate reduction by SRB, were examined for their effects on sulfonate reduction. Molybdate effectively inhibited sulfonate reduction by strain IC1 and selectively inhibited isethionate (but not cysteate) reduction by Desulfitobacterium dehalogenans and Desulfitobacterium sp. strain PCE 1. Desulfitobacterium hafniense, however, grew with both isethionate and cysteate in the presence of molybdate. In contrast, tungstate only partially inhibited sulfonate reduction by both SRB and Desulfitobacterium spp. Similarly, another inhibitor of sulfate reduction, 1,8-dihydroxyanthraquinone, effectively inhibited sulfate reduction by SRB but only partially inhibited sulfonate reduction by both SRB and Desulfitobacterium hafniense.     

Nickel,manganese and copper removal by a mixed consortium of sulfate reducing bacteria at a high COD/sulfate ratio

The use of sulfate-reducing bacteria (SRB) in passive treatments of acidic effluents containing heavy metals has become an attractive alternative biotechnology. Treatment efficiency may be linked with the effluent conditions (pH and metal concentration) and also to the amount and nature of the organic substrate. Variations on organic substrate and sulfate ratios clearly interfere with the biological removal of this ion by mixed cultures of SRB. This study aimed to cultivate a mixed culture of SRB using different lactate concentrations at pH 7.0 in the presence of Ni, Mn and Cu. The highest sulfate removal efficiency obtained was 98 %, at a COD/sulfate ratio of 2.0. The organic acid analyses indicated an acetate accumulation as a consequence of lactate degradation. Different concentrations of metals were added to the system at neutral pH conditions. Cell proliferation and sulfate consumption in the presence of nickel (4, 20 and 50 mg l^?1), manganese (1.5, 10 and 25 mg l^?1) and copper (1.5, 10 and 25 mg l^?1) were measured. The presence of metals interfered in the sulfate biological removal however the concentration of sulfide produced was high enough to remove over 90 % of the metals in the environment. The molecular characterization of the bacterial consortium based on dsrB gene sequencing indicated the presence of Desulfovibrio desulfuricans, Desulfomonas pigra and Desulfobulbus sp. The results here presented indicate that this SRB culture may be employed for mine effluent bioremediation due to its potential for removing sulfate and metals, simultaneously.     

Molecular Phylogenetic and Biogeochemical Studies of Sulfate-Reducing Bacteria in the Rhizosphere of Spartina alterniflora

The population composition and biogeochemistry of sulfate-reducing bacteria (SRB) in the rhizosphere of the marsh grass Spartina alterniflora was investigated over two growing seasons by molecular probing, enumerations of culturable SRB, and measurements of SO₄²⁻ reduction rates and geochemical parameters. SO₄²⁻ reduction was rapid in marsh sediments with rates up to 3.5 μmol ml⁻¹ day⁻¹. Rates increased greatly when plant growth began in April and decreased again when plants flowered in late July. Results with nucleic acid probes revealed that SRB rRNA accounted for up to 43% of the rRNA from members of the domain Bacteria in marsh sediments, with the highest percentages occurring in bacteria physically associated with root surfaces. The relative abundance (RA) of SRB rRNA in whole-sediment samples compared to that of Bacteria rRNA did not vary greatly throughout the year, despite large temporal changes in SO₄²⁻ reduction activity. However, the RA of root-associated SRB did increase from <10 to >30% when plants were actively growing. rRNA from members of the family Desulfobacteriaceae comprised the majority of the SRB rRNA at 3 to 34% of Bacteria rRNA, with Desulfobulbus spp. accounting for 1 to 16%. The RA of Desulfovibrio rRNA generally comprised from <1 to 3% of the Bacteria rRNA. The highest Desulfobacteriaceae RA in whole sediments was 26% and was found in the deepest sediment samples (6 to 8 cm). Culturable SRB abundance, determined by most-probable-number analyses, was high at >10⁷ ml⁻¹. Ethanol utilizers were most abundant, followed by acetate utilizers. The high numbers of culturable SRB and the high RA of SRB rRNA compared to that of Bacteria rRNA may be due to the release of SRB substrates in plant root exudates, creating a microbial food web that circumvents fermentation.     

Analyses of Spatial Distributions of Sulfate-Reducing Bacteria and Their Activity in Aerobic Wastewater Biofilms

The vertical distribution of sulfate-reducing bacteria (SRB) in aerobic wastewater biofilms grown on rotating disk reactors was investigated by fluorescent in situ hybridization (FISH) with 16S rRNA-targeted oligonucleotide probes. To correlate the vertical distribution of SRB populations with their activity, the microprofiles of O₂, H₂S, NO₂⁻, NO₃⁻, NH₄⁺, and pH were measured with microelectrodes. In addition, a cross-evaluation of the FISH and microelectrode analyses was performed by comparing them with culture-based approaches and biogeochemical measurements. In situ hybridization revealed that a relatively high abundance of the probe SRB385-stained cells (approximately 10⁹ to 10¹⁰ cells per cm³ of biofilm) were evenly distributed throughout the biofilm, even in the oxic surface. The probe SRB660-stained Desulfobulbus spp. were found to be numerically important members of SRB populations (approximately 10⁸ to 10⁹ cells per cm³). The result of microelectrode measurements showed that a high sulfate-reducing activity was found in a narrow anaerobic zone located about 150 to 300 μm below the biofilm surface and above which an intensive sulfide oxidation zone was found. The biogeochemical measurements showed that elemental sulfur (S⁰) was an important intermediate of the sulfide reoxidation in such thin wastewater biofilms (approximately 1,500 μm), which accounted for about 75% of the total S pool in the biofilm. The contribution of an internal Fe-sulfur cycle to the overall sulfur cycle in aerobic wastewater biofilms was insignificant (less than 1%) due to the relatively high sulfate reduction rate.     

Sulfate reduction, methanogenesis, and methane oxidation in the upper sediments of the Vistula and Curonian Lagoons, Baltic Sea

Microbiological, biogeochemical, and isotope geochemical investigations of the upper sediments of the Vistula and Curonian lagoons, Baltic Sea, were carried out. High content of organic matter in the sediments was responsible for the high numbers (over 10¹⁰ cells cm^?3) and activity of heterotrophic microorganisms. The calculated integral rates of dark CO₂ assimilation for the upper 30 cm of the sediments varied 12.5 to 38.8 mmol m^?2 day^?1 and were somewhat higher in the Curonian Lagoon than in the Vistula Lagoon. Integral rates of sulfate reduction were higher in the more saline Vistula Lagoon. Rapid consumption of sulfates of the pore water resulted in intensified methanogenesis, with significantly higher rates detected in the silts of the Curonian Lagoon. High rates of methanogenesis in the Curonian Lagoon correlated with higher methane levels in its upper sediments and near-bottom water. The highest rates of methane oxidation were detected in the uppermost sediment horizons (oxidized or slightly reduced), which was an indication of the barrier role of aerobic methanotrophic bacteria. The calculated methane flows from the sediments into the water column were 0.45 and 0.007 mmol m^?2 day^?1 for the Vistula and Curonian Lagoons, respectively. Low methane flow from the sediments of the Curonian Lagoon resulted probably from the specific weather (wind) conditions during sampling. The near-stormy conditions in the Curonian Lagoon caused sediment detachment, resulting in methane release into the water column.     

Detection and Enumeration of Sulphate-Reducing Bacteria in Estuarine Sediments by Competitive PCR

The distribution of sulphate-reducing bacteria (SRB) in the sediments of the Colne River estuary, Essex, UK covering different saline concentrations of sediment porewater was investigated by the use of quantitative competitive PCR. Here, we show that a new PCR primer set and a new quantitative method using PCR are useful tools for the detection and the enumeration of SRB in natural environments. A PCR primer set selective for the dissimilatory sulphite reductase gene (dsr) of SRB was designed. PCR amplification using the single set of dsr-specific primers resulted in PCR products of the expected size from all 27 SRB strains tested, including Gram-negative and positive species. Sixty clones derived from sediment DNA using the primers were sequenced and all were closely related with the predicted dsr of SRB. These results indicate that PCR using the newly designed primer set are useful for the selective detection of SRB from a natural sample. This primer set was used to estimate cell numbers by dsr selective competitive PCR using a competitor, which was about 20% shorter than the targeted region of dsr. This procedure was applied to sediment samples from the River Colne estuary, Essex, UK together with simultaneous measurement of in situ rates of sulphate reduction. High densities of SRB ranging from 0.2 ? 5.7 × 10⁸ cells ml^{? 1} wet sediment were estimated by the competitive PCR assuming that all SRB have a single copy of dsr. Using these estimates cell specific sulphate reduction rates of 10^{? 17} to 10^{? 15} mol of SO₄ ^{2 ?} cell^{? 1} day^{? 1} were calculated, which is within the range of, or lower than, those previously reported for pure cultures of SRB. Our results show that the newly developed competitive PCR technique targeted to dsr is a powerful tool for rapid and reproducible estimation of SRB numbers in situ and is superior to the use of culture-dependent techniques.     

Activity and structure of the sulfate-reducing bacterial community in the sediments of the southern part of Lake Baikal

The rates of sulfate reduction (SR) and the diversity of sulfate-reducing bacteria (SRB) were studied in the sediments of the Posol’skaya Banka elevation in the southern part of Lake Baikal. SR rates varied from 1.2 to 1641 nmol/(dm³ day), with high rates (>600 nmol/(dm³ day)) observed at both deep-water stations and in subsurface silts. Integral SR rates calculated for the uppermost 50 cm of the sediments were higher for gas-saturated and gas hydrate-bearing sediments than in those with low methane content. Enrichment cultures were obtained in Widdel medium for freshwater SRB. Analysis of the 16S rRNA gene fragments from clone libraries obtained from the enrichments revealed the presence of SRB belonged to the genus Desulfosporosinus, with D. lacus as the most closely related member (capable of sulfate, sulfite, and thiosulfate reduction), as well as members of the order Clostridiales.     

Microbial processes of the carbon and sulfur cycles in the Chukchi Sea

The research performed in August 2004 within the framework of the Russian-American Long-term Census of the Arctic (RUSALCA) resulted in the first data concerning the rates of the key microbial processes in the water column and bottom sediments of the Bering strait and the Chukchi Sea. The total bacterial counts in the water column varied from 30 × 10³ cells ml^?1 in the northern and eastern parts to 245 × 10³ cells ml^?1 in the southern part. The methane content in the water column of the Chukchi sea varied from 8 nmol CH₄l^?1 in the eastern part of the sea to 31 nmol CH₄l^?1 in the northern part of the Herald Canyon. Microbial activity occurred in the upper 0–3 cm of the bottom sediments; the methane formation rate varied from 0.25 to 16 nmol CH₄dm^?3 day^?1. The rates of methane oxidation varied from 1.61 to 14.7 nmol CH₄dm^?3 day^?1. The rates of sulfate reduction varied from 1.35 to 16.2 μmol SO ₄ ^2? dm^?1 day^?1. The rate of methane formation in the sediments increased with depth, while sulfate reduction rates decreased (less than 1 μmol SO ₄ ^2? dm^?3 day^?1). These high concentrations of biogenic elements and high rates of microbial processes in the upper sediment layers suggest a specific type of trophic chain in the Chukchi Sea. The approximate calculated balance of methane emission from the water column into the atmosphere is from 5.4 to 57.3 μmol CH₄m^?2 day^?1.     

Analysis of copper corrosion in compacted bentonite clay as a function of clay density and growth conditions for sulfate‐reducing bacteria

Aims: To investigate the relationships between sulfate‐reducing bacteria (SRB), growth conditions, bentonite densities and copper sulfide generation under circumstances relevant to underground, high‐level radioactive waste repositories. Methods and Results: Experiments took place 450 m underground, connected under in situ pressure to groundwater containing SRB. The microbial reduction of sulfate to sulfide and subsequent corrosion of copper test plates buried in compacted bentonite were analysed using radioactive sulfur (³⁵SO₄^2?) as tracer. Mass distribution of copper sulfide on the plates indicated a diffusive process. The relationship between average diffusion coefficients (D_s) and tested density (ρ) was linear. D_s (m² s^?1) = ?0·004 × ρ (kg m^?3) + 8·2, decreasing by 0·2 D_s units per 50 kg m^?3 increase in density, from 1·2 × 10^?11 m² s^?1 at 1750 kg m^?3 to 0·2 × 10^?11 m² s^?1 at 2000 kg m^?3. Conclusions: It is possible that sulfide corrosion of waste canisters in future radioactive waste repositories depends mainly on sulfide concentration at the boundary between groundwater and the buffer, which in turn depends on SRB growth conditions (e.g., sulfate accessibility, carbon availability and electron donors) and geochemical parameters (e.g., presence of ferrous iron, which immobilizes sulfide). Maintaining high bentonite density is also important in mitigating canister corrosion. Significance and Impact of the Study: The sulfide diffusion coefficients can be used in safety calculations regarding waste canister corrosion. The work supports findings that microbial activity in compacted bentonite will be restricted. The study emphasizes the importance of growth conditions for sulfate reduction at the groundwater boundary of the bentonite buffer and linked sulfide production.     

Sulfate reduction and methanogenesis in the Shira and Shunet meromictic lakes (Khakass Republic, Russia)

The biogeochemical and molecular biological study of the chemocline and sediments of saline meromictic lakes Shira and Shunet (Khakass Republic, Russia) was performed. A marked increase in the rates of sulfate reduction and methanogenesis was revealed at the medium depths of the chemocline. The rates of these processes in the bottom sediments decreased with depth. The numbers of Bacteria, Archaea, and of sulfate-reducing bacteria (SRB) were determined by fluorescence in situ hybridization with rRNA specific oligonucleotide probes labeled with horseradish peroxidase and subsequent tyramide signal amplification. In the chemocline, both the total microbial numbers and those of Bacteria were shown to increase with depth. The archaea and SRB were present in almost equal numbers. In the lake sediments, a drastic decrease in microbial numbers with depth was revealed. SRB were found to prevail in the upper sediment layer and archaea in the lower one. This finding correlates with the measured rates of sulfate reduction and methanogenesis.     

Design features of offshore oil production platforms influence their susceptibility to biocorrosion

Offshore oil-producing platforms are designed for efficient and cost-effective separation of oil from water. However, design features and operating practices may create conditions that promote the proliferation and spread of biocorrosive microorganisms. The microbial communities and their potential for metal corrosion were characterized for three oil production platforms that varied in their oil-water separation processes, fluid recycling practices, and history of microbially influenced corrosion (MIC). Microbial diversity was evaluated by 16S rRNA gene sequencing, and numbers of total bacteria, archaea, and sulfate-reducing bacteria (SRB) were estimated by qPCR. The rates of ³⁵S sulfate reduction assay (SRA) were measured as a proxy for metal biocorrosion potential. A variety of microorganisms common to oil production facilities were found, but distinct communities were associated with the design of the platform and varied with different locations in the processing stream. Stagnant, lower temperature (<37 °C) sites in all platforms had more SRB and higher SRA compared to samples from sites with higher temperatures and flow rates. However, high (5 mmol L^?1) levels of hydrogen sulfide and high numbers (10⁷ mL^?1) of SRB were found in only one platform. This platform alone contained large separation tanks with long retention times and recycled fluids from stagnant sites to the beginning of the oil separation train, thus promoting distribution of biocorrosive microorganisms. These findings tell us that tracking microbial sulfate-reducing activity and community composition on off-shore oil production platforms can be used to identify operational practices that inadvertently promote the proliferation, distribution, and activity of biocorrosive microorganisms.